test: Make sure Compute services can use "selfLink" as External value

[yuwenma]

Checklist

• I did not find a related open enhancement request.
• I understand that enhancement requests filed in the GitHub repository are by default low priority.
• If this request is time-sensitive, I have submitted a corresponding issue with GCP support.

Describe the feature or resource

This is to guarantee the backward compatibility when migrating Compute resource to the direct approach.

We need test suites that using "SelfLink" as External value for all cases under compute/v1beta1

More context: #2701 (comment)

Additional information

No response

Importance

No response

[gemmahou]

Compute Forwarding Rule should not have this issue, because we are using our own resolver functions instead of the shared ones, with strict External format restriction: https://github.com/GoogleCloudPlatform/k8s-config-connector/blob/5b1307cd3451ec9fe3c252707f2a2ff32deaa3d9/pkg/controller/direct/compute/refs.go

I can add tests for forwarding rule and other resources.