It's a free Bitbucket plugin. Well, freemium-ish. It requires you have Bitbucket Server running, which is perhaps not the easiest thing to setup, but Atlassian does give out 1-month free trial licenses, or you can use https://developer.atlassian.com/platform/marketplace/timebomb-licenses-for-testing-server-apps/ for a quick 3-hour license.

I would say I'm most proud of this:

    remote: -----
    remote: Push rejected new branch "release/v1.2.X".
    remote: Commits on the new branch MUST arrive via pull-request,
    remote: and the starting-point (2e633566324f9087e93c49b9b0c5fc35601d5add)
    remote: for this new branch has never passed through a pull-request.
    remote: -----