This just convert the file to the new configuration format. The action "delete_head_branch" is added to clean up branches after they are merged.
It has the drawback of having intermediate merge commits for when Mergify merges master before because of this, and then does not squash-merge or rebases it when merging.
Fixes: https://github.com/awesomeWM/awesome/issues/2260 Signed-off-by: Uli Schlachter <psychon@znc.in>