Draft: Improve admin users tabs

What does this MR do and why?

Describe in detail what your merge request does and why.

This MR seeks to improve the Users administration page in several ways.

1. Add an "All" tab, which will allow administrators to search for a user without having to know which tab they would otherwise fit into. (Fixes #17704 (closed))
2. Hide tabs that include no users to avoid requiring a scrollbar to see all tabs in cases where not all categories are used.
3. Move the Email Users, Export Users, and New User button down from the categories tabs to beside the search field. This has three benefits:
   1. Reduces clutter in the categories tabs line.
   2. Prevents these buttons from sitting on top of, and therefore hiding, some categories tabs.
   3. Brings the "New" button in line with the same convention on other administration pages, which all have their respective "New" buttons on the same line as their search.

Screenshots or screen recordings

Current view:

Proposed view:

Proposed view with new tab after blocking:

How to set up and validate locally

1. In GDK, go to the gitlab directory.
2. Switch to this branch: git checkout calebcooper-improve-admin-users-tabs
3. Restart GitLab.
4. Go to the Admin screen and select the Users view on the left.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.