Quick action to approve merge request

Description

(Include problem, use cases, benefits, and/or goals)

Proposal

New quick action for MRs:

/approve

It approves the MR

Overview

I'm a big user of quick actions, and the fact that I can't approve with a quick action is a little annoying

Feature checklist

Make sure these are completed before closing the issue, with a link to the relevant commit.

Edited by Nathan Lincoln