Current pull request commands are: https://wiki.openjdk.org/display/SKARA/Pull+Request+Commands#PullRequestCommands

It has /reviewer and /reviewers to manage the reviewers but these are only limited to credit/remove reviewer or set number of required reviewers.

In some cases, it is desired to have specific reviewer approve the PR as the area lead. The integration should be blocked until the approval from this reviewer.

This request is to provide such slash command. For instance - `/required_reviewer @user` or extend current command like `/reviewer required @user`. Anyone should be able to issue this command on a PR (Current reviewer command can only be issued by the author).