Reminder for open merge requests (E-Mail)
Description
Sometimes some merge requests stay open and are forgotten.
Proposal
Great would be an option to enable automatic e-mail reminder for open merge requests. For example set a time limit (in days) for each project. When the last modification-date of the merge request is older than X days, send an email to the one who's the MR assigned and notify him, that there's an open merge request.