Allow users easy access to items requiring their approval

Problem to solve

Allow users to easily find merge requests on which they are listed as approvers

Further details

When set as an approver and there is ongoing work on a merge request, approvers do not have an easy way to keep track of merge requests that may require their approval (other than email notifications or uncleared todo items)

Proposal

1. Add "Filter by Approver" to the merge request filters
2. Add "Ongoing" notification in the dashboard for open merge requests requiring users approval

What does success look like, and how can we measure that?

1. Users are able to quickly find merge requests on which they are an approver