Leverage repmgr's built-in health checks

```
repmgr node check

Node "fdaa:0:2e26:a7b:c850:fa7a:5336:2":
Server role: OK (node is primary)
Replication lag: OK (N/A - node is primary)
WAL archiving: OK (0 pending archive ready files)
Upstream connection: OK (N/A - node is primary)
Downstream servers: OK (2 of 2 downstream nodes attached)
Replication slots: OK (2 of 2 physical replication slots are active)
Missing physical replication slots: OK (node has no missing physical replication slots)
Configured data directory: OK (configured "data_directory" is "/data/postgresql")
```