Merge Request warning if commiter name is not set

Description

Sometimes new users to an project forget to set the username to a valid one. git uses on Linux something like username@hostname. E.g. pfeifer pfeifer@laniakea which should never go into a repository.

The problem is that currently if the user craft a patchset and the first commit contains the wrong user identification is can quickly comes into the repository and the merger can overlook it. If the wrong commit once is in the repository it is hard to remove it later (colleagues pulled already new branch, ...)

Proposal

If the merge request contains at least one commit with author/submitter in the form username@hostname at least a light warning should be raised at the particular merge request site.

Warning: commit 0xdeadbeef seems to have no valid username!