* Add `--sync-warning` and `--sync-critical`
* Add `sync_replica` to track the number of sync replica in the perf data
* Add `MEMBER-sync` to track if a member is a sync replica in the perf data
This changes requiered python 3.7 which I overlooked at first. I would
like to be able to install the check any patroni server and Patroni
supports python 3.6.