Merge Requests: sort alphabetically

This is a follow on from Epics: Sort Alphabetically?, which added title sorting for epics.

We should add the same support for the Merge Request list, both project lists and global list (https://gitlab.com/dashboard/merge_requests?assignee_username=YOUR_USERNAME)

An MR for this can build directly off the work done for #337135 (closed) (MR: !67234 (merged)).