Split out WIP merge requests

Problem to solve

WIP merge requests clutter the MR view when looking for changes which need review

Intended users

• Code Reviewers
• Developers
• Project Managers

Further details

As a lead developer I often head to /merge_requests to review any pending changes. It's unhelpful when all of the open MRs are WIP and not really ready for feedback.

People tend to create the WIP merge requests because it's the default behaviour for the Create Branch/Create Merge Request button on an issue.

Proposal

• Split the merge request view into "open" and "WIP" tabs.

• Change the fly-out to be a count of open/wip rather than all