Values:
FORWARDING_RULE_TARGET_UNSPECIFIED (0):
Forwarding rule target is unknown.
INSTANCE (1):
Compute Engine instance for protocol
forwarding.
LOAD_BALANCER (2):
Load Balancer. The specific type can be found from
[load_balancer_type]
[google.cloud.networkmanagement.v1.Endpoint.load_balancer_type].
VPN_GATEWAY (3):
Classic Cloud VPN Gateway.
PSC (4):
Forwarding Rule is a Private Service Connect
endpoint.