Add setting to configure the source mode of a data stream

spec/changelog.yml

@@ -24,6 +24,9 @@
   - description: Document and validate `object_type` and `object_type_mapping_type`.
     type: enhancement
     link: https://github.com/elastic/package-spec/pull/417
+  - description: Add setting to configure the source mode of a data stream
+    type: enhancement
+    link: https://github.com/elastic/package-spec/issues/340
 - version: 1.18.0
   changes:
   - description: Update Go runtime to 1.19.1.

spec/integration/data_stream/manifest.spec.yml

@@ -222,5 +222,19 @@ spec:
               type: array
               items:
                 type: string
+        source_mode:
+          description: |-
+            Source mode to use. This configures how the document source (`_source`) is stored
+            for this data stream.
+            If configured as `default`, this mode is not configured and it uses Elasticsearch defaults.
+            If configured as `synthetic`, it doesn't store the source, but tries to rebuild it
+            from the indexed fields when queried.
+            If no configured, users may override the setting from Fleet UI.
+          type: string
+          enum:
+          - "default"
+          - "synthetic"
+          examples:
+          - "synthetic"
   required:
   - title

test/packages/good/data_stream/k8s_data_stream/manifest.yml

@@ -12,3 +12,5 @@ streams:
         default: /server-status
     title: Nginx access logs
     description: Collect Nginx access logs
+elasticsearch:
+  source_mode: "default"

test/packages/time_series/data_stream/example/manifest.yml

@@ -11,6 +11,7 @@ streams:
         default: 10s
 
 elasticsearch:
+  source_mode: "synthetic"
   index_mode: "time_series"
   index_template:
     settings: