Replace usages of _source.mode in documentation (elastic#114743)

We will deprecate the `_source.mode` mapping level configuration
in favor of the index-level `index.mapping.source.mode` setting.
As a result, we go through the documentation and update it to reflect
the introduction of the setting.

Author: salvatore-campagna

docs/plugins/mapper-annotated-text.asciidoc

@@ -167,8 +167,16 @@ duplicates removed. So:
 ----
 PUT idx
 {
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
+    }
+  },
   "mappings": {
-    "_source": { "mode": "synthetic" },
     "properties": {
       "text": {
         "type": "annotated_text",
@@ -215,8 +223,16 @@ are preserved.
 ----
 PUT idx
 {
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
+    }
+  },
   "mappings": {
-    "_source": { "mode": "synthetic" },
     "properties": {
       "text": { "type": "annotated_text", "store": true }
     }

docs/reference/mapping/fields/synthetic-source.asciidoc

@@ -2,7 +2,7 @@
 ==== Synthetic `_source`
 
 IMPORTANT: Synthetic `_source` is Generally Available only for TSDB indices
-(indices that have `index.mode` set to `time_series`). For other indices
+(indices that have `index.mode` set to `time_series`). For other indices,
 synthetic `_source` is in technical preview. Features in technical preview may
 be changed or removed in a future release. Elastic will work to fix
 any issues, but features in technical preview are not subject to the support SLA
@@ -11,15 +11,19 @@ of official GA features.
 Though very handy to have around, the source field takes up a significant amount
 of space on disk. Instead of storing source documents on disk exactly as you
 send them, Elasticsearch can reconstruct source content on the fly upon retrieval.
-Enable this by setting `mode: synthetic` in `_source`:
+Enable this by using the value `synthetic` for the index setting `index.mapping.source.mode`:
 
 [source,console,id=enable-synthetic-source-example]
 ----
 PUT idx
 {
-  "mappings": {
-    "_source": {
-      "mode": "synthetic"
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
     }
   }
 }
@@ -38,7 +42,7 @@ properties when used with synthetic `_source`.
 <<synthetic-source-fields-native-list, Most field types>> construct synthetic `_source` using existing data, most
 commonly <<doc-values,`doc_values`>> and <<stored-fields, stored fields>>. For these field types, no additional space
 is needed to store the contents of `_source` field. Due to the storage layout of <<doc-values,`doc_values`>>, the
-generated `_source` field undergoes <<synthetic-source-modifications, modifications>> compared to original document.
+generated `_source` field undergoes <<synthetic-source-modifications, modifications>> compared to the original document.
 
 For all other field types, the original value of the field is stored as is, in the same way as the `_source` field in
 non-synthetic mode. In this case there are no modifications and field data in `_source` is the same as in the original
@@ -227,10 +231,16 @@ For instance:
 ----
 PUT idx_keep
 {
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
+    }
+  },
   "mappings": {
-    "_source": {
-      "mode": "synthetic"
-    },
     "properties": {
       "path": {
         "type": "object",

docs/reference/mapping/types/aggregate-metric-double.asciidoc

@@ -267,8 +267,16 @@ For example:
 ----
 PUT idx
 {
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
+    }
+  },
   "mappings": {
-    "_source": { "mode": "synthetic" },
     "properties": {
       "agg_metric": {
         "type": "aggregate_metric_double",

docs/reference/mapping/types/boolean.asciidoc

@@ -249,8 +249,16 @@ Synthetic source always sorts `boolean` fields. For example:
 ----
 PUT idx
 {
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
+    }
+  },
   "mappings": {
-    "_source": { "mode": "synthetic" },
     "properties": {
       "bool": { "type": "boolean" }
     }

docs/reference/mapping/types/date.asciidoc

@@ -130,7 +130,7 @@ The following parameters are accepted by `date` fields:
 <<ignore-malformed,`ignore_malformed`>>::
 
     If `true`, malformed numbers are ignored. If `false` (default), malformed
-    numbers throw an exception and reject the whole document.  Note that this
+    numbers throw an exception and reject the whole document. Note that this
     cannot be set if the `script` parameter is used.
 
 <<mapping-index,`index`>>::
@@ -248,8 +248,16 @@ Synthetic source always sorts `date` fields. For example:
 ----
 PUT idx
 {
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
+    }
+  },
   "mappings": {
-    "_source": { "mode": "synthetic" },
     "properties": {
       "date": { "type": "date" }
     }

docs/reference/mapping/types/date_nanos.asciidoc

@@ -160,8 +160,16 @@ Synthetic source always sorts `date_nanos` fields. For example:
 ----
 PUT idx
 {
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
+    }
+  },
   "mappings": {
-    "_source": { "mode": "synthetic" },
     "properties": {
       "date": { "type": "date_nanos" }
     }

docs/reference/mapping/types/flattened.asciidoc

@@ -334,8 +334,16 @@ For example:
 ----
 PUT idx
 {
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
+    }
+  },
   "mappings": {
-    "_source": { "mode": "synthetic" },
     "properties": {
       "flattened": { "type": "flattened" }
     }
@@ -367,8 +375,16 @@ For example:
 ----
 PUT idx
 {
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
+    }
+  },
   "mappings": {
-    "_source": { "mode": "synthetic" },
     "properties": {
       "flattened": { "type": "flattened" }
     }
@@ -407,8 +423,16 @@ For example:
 ----
 PUT idx
 {
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
+    }
+  },
   "mappings": {
-    "_source": { "mode": "synthetic" },
     "properties": {
       "flattened": { "type": "flattened" }
     }

docs/reference/mapping/types/geo-point.asciidoc

@@ -229,8 +229,16 @@ longitude) and reduces them to their stored precision. For example:
 ----
 PUT idx
 {
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
+    }
+  },
   "mappings": {
-    "_source": { "mode": "synthetic" },
     "properties": {
       "point": { "type": "geo_point" }
     }

docs/reference/mapping/types/ip.asciidoc

@@ -170,8 +170,16 @@ Synthetic source always sorts `ip` fields and removes duplicates. For example:
 ----
 PUT idx
 {
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
+    }
+  },
   "mappings": {
-    "_source": { "mode": "synthetic" },
     "properties": {
       "ip": { "type": "ip" }
     }

docs/reference/mapping/types/keyword.asciidoc

@@ -188,8 +188,16 @@ For example:
 ----
 PUT idx
 {
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
+    }
+  },
   "mappings": {
-    "_source": { "mode": "synthetic" },
     "properties": {
       "kwd": { "type": "keyword" }
     }
@@ -218,8 +226,16 @@ are preserved. For example:
 ----
 PUT idx
 {
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
+    }
+  },
   "mappings": {
-    "_source": { "mode": "synthetic" },
     "properties": {
       "kwd": { "type": "keyword", "store": true }
     }
@@ -248,8 +264,16 @@ For example:
 ----
 PUT idx
 {
+  "settings": {
+    "index": {
+      "mapping": {
+        "source": {
+          "mode": "synthetic"
+        }
+      }
+    }
+  },
   "mappings": {
-    "_source": { "mode": "synthetic" },
     "properties": {
       "kwd": { "type": "keyword", "ignore_above": 3 }
     }