Check necesisty of site_manager_health metric

[Imadzuma]

Now we have site_manager_health metric, that shows, if health check passed:
https://github.com/Netcracker/DRNavigator/blob/main/site-manager.py#L34

Additionally after #123 will add paas_geo_monitor_health metric.

Those metrics are 0 by default and become to be 1 after the first successful health check, but not on the contrary.

Need to check, if kubernetes/prometheus has more appropriate mechanisms for health check, e.g. metrics for readness/liveness probes.