Use 201 status code where appropriate for APIv4 (#5903)

api4/post.go

@@ -52,6 +52,7 @@ func createPost(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	w.WriteHeader(http.StatusCreated)
 	w.Write([]byte(rp.ToJson()))
 }