DEV: Add meta_topic_id plugin metadata (#23838)

For the admin plugin list we want to be able to link to
a meta topic for plugins, but we have no standard way to
do this at the moment. This adds support for meta_topic_id
alongside other plugin metadata like authors, URL etc,
that gets built into a Meta topic URL in the serializer.

app/assets/javascripts/admin/addon/models/admin-plugin.js

@@ -21,6 +21,7 @@ export default class AdminPlugin {
     this.name = args.name;
     this.url = args.url;
     this.version = args.version;
+    this.metaUrl = args.meta_url;
   }
 
   get settingCategoryName() {