[CCR] Resume follow Api should not require a request body (#37217)

Closes #37022

x-pack/plugin/ccr/qa/rest/src/test/resources/rest-api-spec/test/ccr/follow_and_unfollow.yml

@@ -52,7 +52,6 @@
   - do:
       ccr.resume_follow:
         index: bar
-        body: {}
   - is_true: acknowledged
 
   - do:

x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/rest/RestResumeFollowAction.java

@@ -37,8 +37,14 @@ public class RestResumeFollowAction extends BaseRestHandler {
     }
 
     static Request createRequest(RestRequest restRequest) throws IOException {
-        try (XContentParser parser = restRequest.contentOrSourceParamParser()) {
-            return Request.fromXContent(parser, restRequest.param("index"));
+        if (restRequest.hasContentOrSourceParam()) {
+            try (XContentParser parser = restRequest.contentOrSourceParamParser()) {
+                return Request.fromXContent(parser, restRequest.param("index"));
+            }
+        } else {
+            Request request = new Request();
+            request.setFollowerIndex(restRequest.param("index"));
+            return request;
         }
     }
 }

x-pack/plugin/src/test/resources/rest-api-spec/api/ccr.resume_follow.json

@@ -15,7 +15,7 @@
     },
     "body": {
       "description" : "The name of the leader index and other optional ccr related parameters",
-      "required" : true
+      "required" : false
     }
   }
 }