Restrict selected pull request merge strategies in repository settings by publishing a cancellable event

We have customers that would like to restrict the merge strategies a repository/project admin can choose from in the pull request repository settings. This is so administrators can enforce a subset of merge strategies company wide.

Currently the only way to do this is through some JavaScript loaded onto the page which hides the merge strategies from the repository/project admin. However they are still able to enable/disable through the REST API.

We have had a few customers request this for ScriptRunner for Bitbucket Server and currently there is no better way to do this.

It would be good to publish a cancellable event when the selected merge strategies are updated for a particular repository, it could contain the repository and the original and the updated merge strategies. Then we can prevent some strategies from being enabled based on some logic the user defines which would also be more flexible and faster than the user manually restricting them per repository.