Track UI message improvements for Create in 14.6
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### Problem to solve
As a follow-up to https://gitlab.com/gitlab-org/gitlab/-/issues/346051 we should track the changes to error messages that land in 14.6. I can link this issue to the epic https://gitlab.com/groups/gitlab-org/-/epics/6436, so we have a chain from the individual MRs back up to the original plan.
### Further details
Spreadsheet of [all work](https://docs.google.com/spreadsheets/d/15pq5iPmBNzarepJJkqxLHmEZVvdzuQ4SdRQBe5UBGLQ/edit#gid=1603674567) is available.
### Proposal
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### Who can address the issue
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### Other links/references
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