Add pre-commit hooks to call into various ci-fairy functionality

Supersedes !78 (closed), changes to that MR:

• add ci-fairy check-commits --guess-default-branch to make it guess between master/main. This avoids having to configure the hook don't pass filenames to the check-commits hook
• move lint to stage push, I think that's enough except in very rare cases
• add a hook for ci-fairy generate-template

cc @nimrod