MR should be unacceptable

ZD: https://gitlab.zendesk.com/agent/tickets/15788

Expected Behavior

If a commit message of a Merge Request does not match the configured "Commit Message" in the Git Hooks project settings, the merge request should not be clickable and a text message should be shown accordingly.

Observed Behavior

The merge request is still acceptable by any user but the commit won't be pushed to the target branch (which is for sure good). The button will show an infinite amount of time the message "Merge in progress".

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Similar to #305 (closed) /cc @brodock can you take a look at this?