Remove Stale Branches

[MichaelCordingley]

Description: Automatically remove branches that are not associated with an open issue and are more than X days stale.

Previously described in https://github.com/actions/stale/issues/620, which ironically closed due to staleness.

Justification: Branches are another form of cruft that builds up and becomes stale.

Are you willing to submit a PR? I'm probably not the best person to do so, else I would