Re-add the external health monitor deployment once the new health-monitor code merges

[torredil]

in #678 we are removing the health monitor sidecar deployment and some tests as part of moving to the new volume health RPCs. Once the updated health-monitor is available, the deployment and tests should be brought back so that path is covered again.

[torredil]

/assign

[torredil]

This has a dependency on kubernetes-csi/external-health-monitor#376