[OpenAPI] Add more externalDocs and x-model values

Author: lcawl

docs/overlays/elasticsearch-shared-overlays.yaml

@@ -1076,6 +1076,11 @@ actions:
       x-model: true
       externalDocs:
         url: https://www.elastic.co/guide/en/elasticsearch/reference/master/collapse-search-results.html
+  - target: "$.components['schemas']['_global.msearch:MultisearchBody'].properties"
+    description: Add x-model
+    update:
+      aggregations:
+        x-model: true
 # Examples
   - target: "$.components['requestBodies']['async_search.submit']"
     description: "Add example for asynch search submit request"

output/openapi/elasticsearch-openapi.json

@@ -68,7 +68,10 @@ export class MultisearchHeader {
 
 // We should keep this in sync with the normal search request body.
 export class MultisearchBody {
-  /** @aliases aggs */ // ES uses "aggregations" in serialization
+  /**
+   * @aliases aggs
+   * @ext_doc_id search-aggregations
+   */ // ES uses "aggregations" in serialization
   aggregations?: Dictionary<string, AggregationContainer>
   collapse?: FieldCollapse
   /**