Moved validation integration test into 10_basic suite.

Author: adhulipa

x-pack/plugin/src/test/resources/rest-api-spec/test/watcher/put_watch/10_basic.yml

@@ -36,3 +36,16 @@
             }
           }
   - match: { _id: "my_watch" }
+
+---
+"Test empty body is rejected by put watch":
+  - do:
+      cluster.health:
+          wait_for_status: yellow
+
+  - do:
+      catch: bad_request
+      xpack.watcher.put_watch:
+        id: "my_watch"
+  - match: { error.root_cause.0.type: "action_request_validation_exception" }
+  - match: { error.root_cause.0.reason: "Validation Failed: 1: request body is missing;" }