Make creating MRs from Issues more findable

Problem to solve

The current placement of the "Create merge request" action has low visibility, making it hard to find and out of sync with its display as a primary action.

Concepts

As an action related to the Issue object itself, rather than a widget within the Issue, the Create merge request action makes sense grouped closer to other Issue actions such as Close (action button) or New related issue (option in actions menu).

Alternately, MRs appear below the description, and are related to other relationship widgets, so treating this similar to adding tasks or linked items could be relevant. The branch/MR relationship is a bit different (when closed by, as is automatically the case using the create MR button) as a representation of the same work, rather than just related content.

Design to be added