[OpenAPI] Edit mget API

Author: lcawl

docs/overlays/elasticsearch-shared-overlays.yaml

@@ -181,8 +181,6 @@ actions:
           x-displayName: Script - Get languages
         - name: search
           x-displayName: Search
-        - name: msearch
-          x-displayName: Search - Multi search
         - name: scroll
           x-displayName: Search - Scroll
         - name: terms_enum

specification/_global/msearch/MultiSearchRequest.ts

@@ -23,10 +23,28 @@ import { long } from '@_types/Numeric'
 import { RequestItem } from './types'
 
 /**
+ * Run multiple searches.
+ *
+ * The format of the request is similar to the bulk API format and makes use of the newline delimited JSON (NDJSON) format.
+ * The structure is as follows:
+ *
+ * ```
+ * header\n
+ * body\n
+ * header\n
+ * body\n
+ * ```
+ *
+ * This structure is specifically optimized to reduce parsing if a specific search ends up redirected to another node.
+ *
+ * IMPORTANT: The final line of data must end with a newline character `\n`.
+ * Each newline character may be preceded by a carriage return `\r`.
+ * When sending requests to this endpoint the `Content-Type` header should be set to `application/x-ndjson`.
  * @rest_spec_name msearch
  * @availability stack since=1.3.0 stability=stable
  * @availability serverless stability=stable visibility=public
  * @index_privileges read
+ * @doc_tag search
  */
 export interface Request extends RequestBase {
   path_parts: {