This PR adds a new `--run-script-post-backup` option that allows running a script after the main backup operation has completed, but before locking, compacting and verification is done.
The use for this is intended for cases where you want to stop or pause some service, run a backup, and then resume the service. Prior to this PR you would need to wait for the entire backup operation to complete, but with the new option you can resume as soon as the source data is no longer needed.
