Resolve "View labels when editing labels in sidebar and board sidebar"

What does this MR do?

Makes the current labels stay visible as we're editing them.

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

frontend I changed the issue created on the rspec to have one extra label on all tests in that suite. Is there a problem in that? (https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/18380/diffs#2dbb48f9533e04fc3846454cb210350e7e70e635_11_10)

Why was this MR needed?

When user is editing the labels, the ones that already there are unseen.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #34262 (closed)