Allow fields in BulkOperation to be optional

    https://opensearch.org/docs/1.3/api-reference/document-apis/bulk/#request-body
    > All actions support the same metadata: _index, _id, and _require_alias. If you don’t provide an ID, OpenSearch generates one automatically, which can make it challenging to update the document at a later time.

Signed-off-by: Cameron Durham <u64.cam@gmail.com>

api/types.d.ts

@@ -40,12 +40,12 @@ export interface BulkIndexOperation extends BulkOperation { }
 export interface BulkIndexResponseItem extends BulkResponseItemBase { }
 
 export interface BulkOperation {
-  _id: Id;
-  _index: IndexName;
-  retry_on_conflict: integer;
-  routing: Routing;
-  version: VersionNumber;
-  version_type: VersionType;
+  _id?: Id;
+  _index?: IndexName;
+  retry_on_conflict?: integer;
+  routing?: Routing;
+  version?: VersionNumber;
+  version_type?: VersionType;
 }
 
 export interface BulkOperationContainer {