[SPEC] Specify bulk format for body in bulk, msearch, mpercolate

rest-api-spec/api/bulk.json

@@ -51,7 +51,8 @@
     },
     "body": {
       "description" : "The operation definition and data (action-data pairs), separated by newlines",
-      "required" : true
+      "required" : true,
+      "serialize" : "bulk"
     }
   }
 }

rest-api-spec/api/mpercolate.json

@@ -34,7 +34,8 @@
     },
     "body": {
       "description": "The percolate request definitions (header & body pair), separated by newlines",
-      "required": true
+      "required": true,
+      "serialize" : "bulk"
     }
   }
 }

rest-api-spec/api/msearch.json

@@ -25,7 +25,8 @@
     },
     "body": {
       "description": "The request definitions (metadata-search request definition pairs), separated by newlines",
-      "required" : true
+      "required" : true,
+      "serialize" : "bulk"
     }
   }
 }