Values:
EVENT_TYPE_UNSPECIFIED (0):
Event is not specified.
IDLE (1):
The instance / runtime is idle
HEARTBEAT (2):
The instance / runtime is available.
This event indicates that instance / runtime
underlying compute is operational.
HEALTH (3):
The instance / runtime health is available.
This event indicates that instance / runtime
health information.
MAINTENANCE (4):
The instance / runtime is available.
This event allows instance / runtime to send
Host maintenance information to Control Plane.
https://cloud.google.com/compute/docs/gpus/gpu-host-maintenance