Values:
HEALTH_STATE_UNSPECIFIED (0):
The instance substate is unknown.
HEALTHY (1):
The instance is known to be in an healthy
state (for example, critical daemons are
running) Applies to ACTIVE state.
UNHEALTHY (2):
The instance is known to be in an unhealthy
state (for example, critical daemons are not
running) Applies to ACTIVE state.
AGENT_NOT_INSTALLED (3):
The instance has not installed health
monitoring agent. Applies to ACTIVE state.
AGENT_NOT_RUNNING (4):
The instance health monitoring agent is not
running. Applies to ACTIVE state.