Add new field migrate_from under policy_templates

spec/changelog.yml

@@ -15,6 +15,9 @@
     - description: Require defining agent version constraints in input and integration packages.
       type: breaking-change
       link: https://github.com/elastic/package-spec/pull/999
+    - description: Add definition for migrate_from field.
+      type: enhancement
+      link: https://github.com/elastic/package-spec/pull/1021
 - version: 3.5.3-next
   changes:
     - description: Make support for alert rule templates more permissive.

spec/integration/data_stream/manifest.spec.yml

@@ -69,7 +69,7 @@ spec:
           type:
             description: >
               Data type of variable.
-              
+
               A duration type is a sequence of decimal numbers, each with a unit
               suffix, such as "60s", "1m" or "2h45m".
               Duration values must follow these rules:
@@ -117,7 +117,7 @@ spec:
           secret:
             description: >
               Specifying that a variable is secret means that Kibana will store the value
-              separate from the package policy in a more secure index. 
+              separate from the package policy in a more secure index.
               This is useful for passwords and other sensitive information.
               One caveat is that secrets are write-only, once a user writes a secret var
               they cannot read it again, only overwrite it.
@@ -360,15 +360,15 @@ spec:
               description: >
                 Turn the support for subobjects on or off in the mapping
                 configuration for the data stream.
-                
+
                 By default, it's set to `true`, enabling Elasticsearch to
                 expands fields that contain dots in their names
                 to their corresponding object structure.
 
                 Setting it to `false` restricts objects
                 from holding subobjects, enabling storing documents
                 with dot-contained field names and common prefixes.
-                
+
                 It is still possible to send documents that have
                 objects to a data stream that has set subobjects
                 to `false`.
@@ -378,16 +378,16 @@ spec:
                 PUT my-index-000001
                 {
                   "mappings": {
-                    "subobjects": false 
+                    "subobjects": false
                   }
                 }
 
                 PUT my-index-000001/_doc/metric_1
                 {
-                  "time" : "100ms", 
+                  "time" : "100ms",
                   "time.min" : "10ms",
                   "time.max" : "900ms"
-                }                
+                }
 
                 Before disabling subobjects, consider the following implications:
 
@@ -403,7 +403,7 @@ spec:
 
                 For comprehensive details on subobjects, refer to
                 the Elasticsearch documentation [^2].
-                
+
 
                 [^1]: Auto-flattening limitations are documented at:
                 https://www.elastic.co/guide/en/elasticsearch/reference/master/subobjects.html#_auto_flattening_object_mappings

spec/integration/manifest.spec.yml

@@ -124,7 +124,7 @@ spec:
           - notification
           # Metrics, logs, and traces collection
           - observability
-          # OpenTelemetry 
+          # OpenTelemetry
           - opentelemetry
           # Operating system monitoring
           - os_system
@@ -630,6 +630,13 @@ spec:
                     - ["default"]
                     - ["agentless"]
                     - ["default", "agentless"]
+                migrate_from:
+                  description: >
+                    Previous variable name to migrate value from.
+                    This is useful when renaming variables while maintaining existing user values.
+                  type: string
+                  examples:
+                    - old_input_name
                 required_vars:
                   $ref: "./data_stream/manifest.spec.yml#/definitions/required_vars"
                 vars: