Follow-up to https://github.com/zed-industries/zed/pull/37489

Notification panel settings were always missing the content, hence this
PR adds it. After #37489, the use of the same content twice broke
things, which currently makes the notification panel non-configurable on
Nightly. This PR fixes this.

There once was an issue about the documentation for the panel being
wrong as well. However, I was just unable to find that sadly.

Release Notes:

- N/A