title: Restrict github merge type by source branch
body: <p>By default, github allows you to squash, merge or rebase when merging a PR.
  Is it possible to conditionally restrict the allowed merge types?</p>
  
  <p>In our team, we typically squash PRs onto our feature (or develop) branches.
  However, when merging feature branches back into develop (or develop -> feat/*) we want to use a merge commit.</p>
  
  <p>It is straightforward enough to choose the correct button in the github UI, be we occasionally have someone choose the wrong option by mistake and need to repair the repo afterwards.</p>
  
  <p>Is there any way to restrict the allowed options in github?
  This could either by branch name (e.g. merging from feat/* or develop must be a merge)?</p>