I have successfully configured a Jenkins multi-branch pipeline to build my project which is hosted on Bitbucket. I have separate pipeline requirements for the "develop" and "release" branches, and for merge requests. These are now working correctly (except for a surplus "PR-***" job whenever a Bitbucket PR is triggered).
My remaining issue is: In old-style Jenkins I used Bitbucket Pull Request plugin, which had a feature "Comment phrase to trigger build". So in the event of a flaky unit test etc I could issue the trigger phrase as a comment in the pull request, and it would be rebuilt.
How can I achieve this behaviour on a multi-branch pipeline?