elasticsearch-specification update

Update code based on https://github.com/elastic/elasticsearch-specification/blob/main/output/schema/schema.json
from Wed Mar  6 00:33:29 UTC 2024.

Author: github-actions[bot]

elasticsearch-ingest-node.schema.json

@@ -1230,14 +1230,11 @@
         },
         "_meta": {
           "$ref": "#/$defs/Metadata",
-          "description": "Arbitrary metadata about the ingest pipeline. This map is not automatically generated by Elasticsearch. Required."
+          "description": "Arbitrary metadata about the ingest pipeline. This map is not automatically generated by Elasticsearch."
         }
       },
       "additionalProperties": false,
-      "type": "object",
-      "required": [
-        "_meta"
-      ]
+      "type": "object"
     },
     "PipelineProcessor": {
       "properties": {