k8s: fix incorrect EndpointSlice API version

[ysksuzuki]

This PR fixes a bug that k8s watcher incorrectly chooses the discovery/v1beta1 EndpointSlice in environments where discovery/v1 EndpointSlice is available. The agent doesn't wait for the discovery/v1 EndpointSlice to be received on its restart and ends up removing live services because of this bug.

The issue happens in the following scenario:

1. The agent initializes and runs the informers for Service and EndpointSlice.
2. The reflectors list the resources from kube-apiserver and replace DeltaFIFO.
3. The informers pop items from the DeltaFIFO and call the onAdd handler one by one.
4. If the Service handler is called first, ServiceCache.UpdateService doesn't emit the UpdateService event, because the service is not ready. (No backend)
5. The EndpointSlice handler is called next, ServiceCache.updateEndpoints emits UpdateService event.
6. The agent doesn't wait until the event triggered at step 5 is processed, and calls SyncWithK8sFinished.
7. The agent removes live services because it hasn't heard about them. (It is supposed to hear about those services in the event process triggered at step 5)

This issue doesn't persist in v1.14 and later because K8sAPIGroupEndpointSliceOrEndpoint is used in those versions. The affected versions are v1.13 and v1.12.

Fixes: #27215

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[christarazi]

/test-backport-1.13

Job 'Cilium-PR-K8s-1.25-kernel-4.19' failed:

Click to show.

Test Name

K8sDatapathServicesTest Checks E/W loadbalancing (ClusterIP, NodePort from inside cluster, etc) Tests NodePort inside cluster (kube-proxy) 

Failure Output

FAIL: Request from testclient-rlbxb pod to service tftp://[fd04::11]:31994/hello failed

Jenkins URL: https://jenkins.cilium.io/job/Cilium-PR-K8s-1.25-kernel-4.19/818/

If it is a flake and a GitHub issue doesn't already exist to track it, comment /mlh new-flake Cilium-PR-K8s-1.25-kernel-4.19 so I can create one.

Then please upload the Jenkins artifacts to that issue.

[christarazi]

Good catch!

[ysksuzuki]

/test-1.25-4.19

[nebril]

I think we can merge this one, but we also need this change in 1.12, right?