Setting url parts as required to reflect the code base (#27263)

rest-api-spec/src/main/resources/rest-api-spec/api/indices.exists_alias.json

@@ -12,6 +12,7 @@
         },
         "name": {
           "type" : "list",
+          "required" : true,
           "description" : "A comma-separated list of alias names to return"
         }
       },

rest-api-spec/src/main/resources/rest-api-spec/api/reindex_rethrottle.json

@@ -8,6 +8,7 @@
       "parts": {
         "task_id": {
           "type": "string",
+          "required" : true,
           "description": "The task id to rethrottle"
         }
       },

rest-api-spec/src/main/resources/rest-api-spec/api/tasks.get.json

@@ -8,6 +8,7 @@
       "parts": {
         "task_id": {
           "type": "string",
+          "required" : true,
           "description": "Return the task with specified id (node_id:task_number)"
         }
       },