feat(Tailwind): remove ring Tailwind classes and adjust outline colors

What does this MR do?

Related to #2997 (comment 2205225819)

• We have gl-focus so let's remove Tailwind CSS ring classes for now to avoid confusion. In the future we can consider migrating to these Tailwind CSS ring classes.
  • gl-ring-* classes are not used in any consuming GitLab projects. But this should still be considered a breaking change.
• Updates the outline-color to only have --gl-focus-ring-outer-color so we are consistent. If we are using a different outline color then we are not following Pajamas guidelines.
• Adds a gl-focus-inset class to match the behavior of the mixin when called like gl-focus($inset: true)

Screenshots or screen recordings

This is what the updated Tailwind docs will look like (once updated):

Integration merge requests

• GitLab: mr_url
• CustomersDot: mr_url
• Status Page: mr_url