Resolve "System level labels UI broken"

What does this MR do?

Fixes the UI of System level labels in the admin.

• Also adds an adaptation to small screens to make it comfortable to see the labels both at a project and at a system level.

Are there points in the code the reviewer needs to double check?

I added one commit (easily removable) that improves the way this list displays in small screens. We can either iterate a bit here (as long as it doesn't go over the freeze) or we can remove it from here and open a separate issue. I leave that to the UX review.

Why was this MR needed?

When we re-did the list of labels in the project level, we didn't consider the admin list of labels at a system level.

Screenshots (if relevant)

Before	After

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them

What are the relevant issue numbers?

Closes #48456 (closed)