feat: add --default-branch-only cmdline option
Add a cmdline option to only mirror the default branch of a given action between github.com and the target GitHub Enterprise instance, though still mirroring all tags. This is particularly useful when syncing verified publisher actions that may contain a large number of stale and/or ongoing development branches and we only ever really want to sync the tagged releases from the main branch for consumption. This additionally avoids the "triggered actions storm" that can happen when syncing many branches.
Contributes-to: actions/actions-sync#12
@shawnHartsell are you happy to assign a reviewer from amongst the codeowners?
Pinging @shawnHartsell - any chance this could be merged in?