Configuration: Branches to be skipped for deletion, rebase, etc

[HaywardMorihara]

See https://github.com/HaywardMorihara/gh-tidy/issues/41 for the genesis of the idea

Make it so users can opt-out of a tidy step, because not everyone will want the same things

Different developers use branches in different ways - it would be nice if they configure gh tidy so that they could specify (in a local file) what branches should be considered for deletion, rebase, or any other tidy actions

[HaywardMorihara]

https://github.com/HaywardMorihara/gh-tidy/issues/46 is another place where this would be nice