Display an error message if the rollback of an environment fails

Proposal

A rollback of an environment can fail if the job was retried, archived or deployment rejected (see code here). But, clicking the Rollback environment button does not produce any error messages. It simply refreshes the page as if the rollback succeeded. It'd be better if the page showed the actual failure reason.

Feature requested by a 612 seater large GitLab Premium customer . ZD ticket for internal reference: #593549.