Conformance: Set the Address field in Gateway Status

[kate-osborn]

The conformance tests expect the addresses field in the GatewayStatus to be set by the controller. The tests use the first IP address in addresses to send requests to the data plane to verify the routes are working properly.

Since this issue aims to unblock the conformance tests, we will use the Pod IP of the NKG Pod only.

Acceptance Criteria:

• Set the GatewayStatus.addresses field to the Pod IP of the NKG Pod.
• Verify the conformance test helper WaitForGatewayAddress succeeds.
• Update the gateway API compatibility doc