Retry button for halted migrations

Problem

No way to rerun migrations that are halted. For example, if the issues migration encountered a problem and retried many times it will be halted, but there's no indication that this migration has failed and no easy way to restart it.

Solution

Need a button next to the halted message to unhalt and retry last failed.

Technical details

If a migration is halted, it's marked as halted: true in the gitlab-development-migrations. We probably want to remove the entire record for it to be picked up again.