refactor: only cache commands from own user (#6161)

src/structures/ApplicationCommand.js

@@ -19,6 +19,12 @@ class ApplicationCommand extends Base {
      */
     this.id = data.id;
 
+    /**
+     * The parent application's id
+     * @type {Snowflake}
+     */
+    this.applicationId = data.application_id;
+
     /**
      * The guild this command is part of
      * @type {?Guild}