[Backport 8.12] Add support for subobjects property (#2446)

(cherry picked from commit 4e97d99)

Co-authored-by: Quentin Pradet <[email protected]>

Author: github-actions[bot]

output/openapi/elasticsearch-serverless-openapi.json

@@ -48,6 +48,7 @@ export class TypeMapping {
   _source?: SourceField
   runtime?: Dictionary<string, RuntimeField>
   enabled?: boolean
+  subobjects?: boolean
   /**
    * @availability stack since=7.16.0
    * @availability serverless

output/schema/schema.json

@@ -45,6 +45,7 @@ export class NestedProperty extends CorePropertyBase {
 
 export class ObjectProperty extends CorePropertyBase {
   enabled?: boolean
+  subobjects?: boolean
   type?: 'object'
 }