Enabled Ember's template-only-gimmer-components feature

no issue

- template-only components (eg, `<GhMembersListItem>`) will now use a glimmer class rather than regular component class for their automatically-created backing classes

config/optional-features.json

@@ -1,4 +1,5 @@
 {
   "application-template-wrapper": false,
-  "jquery-integration": true
+  "jquery-integration": true,
+  "template-only-glimmer-components": true
 }