Add keyboard shortcut for change reviewer in merge request as "v"
<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=322969) </details> <!--IssueSummary end--> <!-- This template is a great use for issues that are feature::additions or technical tasks for larger issues.--> Since 13.7 it is [possible](https://about.gitlab.com/blog/2020/10/13/merge-request-reviewers/) to assign a reviewer to a merge request. Using this feature extensively it would be helpfull to set a keyboard shortcut for it. E.g. analog to `a` for [change assignee](https://docs.gitlab.com/ee/user/shortcuts.html#issues-and-merge-requests). ### Proposal Add keyboard shortcut for change reviewer in merge request. As `r` ist already assigned, next candidate can be `v` (reViewer). <!-- Use this section to explain the feature and how it will work. It can be helpful to add technical details, design proposals, and links to related epics or issues. --> <!-- Consider adding related issues and epics to this issue. You can also reference the Feature Proposal Template (https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Feature%20proposal.md) for additional details to consider adding to this issue. Additionally, as a data oriented organization, when your feature exits planning breakdown, consider adding the `What does success look like, and how can we measure that?` section. -->
issue