Issue Summary

When editing an existing template that is still on the legacy template editor, it won't be possible to mention users.

Steps to Reproduce

1. Edit a template on the legacy template editor
2. Try to @mention someone

Expected Results

The list of users should be shown, allowing users to be mentioned.

Actual Results

• The list of users isn't shown, preventing anyone from being mentioned.
• When trying to use the mention from the macro browser, a "No Macro metadata" message is displayed:
  

Workaround

Create a new template using the new template editor.