Add a message in the project homepage in case the mirror repository fails

Description

We can mirror a repository in GitLab (push and pull).

When the mirror is pulled, we already display a warning message when it fails. However, when we push to a mirror, we don't notify the project owner that something is wrong. The only way to know is to go to this Mirror repository setting page.

Proposal

Display a message at the top of the project's homepage to show when a project can't be pushed to the remote repository.