Archive Labels: Prevent adding archived labels

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What does this MR do and why?

#4233 added the attribute :archived to Labels and !198689 (merged) made sure that archived labels do not show up in the auto completion when using /label ~.... This MR makes sure that you cannot add archived labels when typing them in by hand in /label ... or /relabel ... commands.

The related issue is Remove archived labels from quick actions and a... (#554226 - closed).

🛠️ with ❤️ at Siemens

References

• Remove archived labels from quick actions and a... (#554226 - closed)
• Archived labels (#4233)
• Hide archived labels from auto completion (!198689 - merged)

Screenshots or screen recordings

How to set up and validate locally

1. Enable feature flag with rails c:

 Feature.enable(:labels_archive)

2. Archive a label: Go to Any project > Manage > Labels and edit a label in the three dot dropdown. Check the Archived checkbox and save the label.
3. Now add a comment to any issue with /label ~<your archived label> or /relabel ~<your archived label>. You should see that the label is not applied and there is an error instead.

MR acceptance checklist

checklist

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the javascript style guides
• Conforms to the database guides

Related to #4233