Replace deprecated Stable9 Base theme (with a Bootstrap Base Theme)

Problem/Motivation

Please see: #3567667: Deprecate Stable9

Steps to reproduce

Proposed resolution

I tried using https://www.drupal.org/project/bootstrap5 as the base theme, and it seems to have improved things.
Of course, there are alternative Bootstrap base themes to consider, but Bootstrap5 seems fine. It's not bloated with SDCs (nothing against SDCs, but I don't think we will benefit from them in this project), etc., and it's pretty straightforward.

Remaining tasks

• [x] Replace base them in info file
• [ ] Remove duplicate theme settings
• [ ] Alter theme setting for theme mode 'auto' (BS5 theme only provides dark and light)
• [ ] Unset further not required settings from the BS5 theme
• [x] The Bootstrap Lib is loaded twice, disable the BS5 theme library in adminlte.info.yml:
  
  

  libraries-override:
    bootstrap5/global-styling: false
    bootstrap5/bootstrap5-js-latest: false
      

• [x] Override the bootstrap5 themes ckeditor_stylesheets (info file).
  • [ ] We can override the base themes ckeditor styles, but we can't replace them #3458077: Allow overriding/disabling base theme's ckeditor5-stylesheets value
• [x] Add Dependency (composer.json / .info)

User interface changes

API changes

Data model changes