E2E / integration test for AdminKubeconfigRequest feature

[timebertt]

How to categorize this issue?

/area testing
/kind enhancement

What would you like to be added:

An automated test for the AdminKubeconfigRequest feature. Could be a new e2e test or a step in one of the existing e2e tests or an integration test.

Why is this needed:

AdminKubeconfigRequest was promoted to GA in #5511.
However, there is no automated test for verifying the functionality. Hence, the functionality has to be tested manually in order to prevent bugs and regressions.

[timebertt]

@acumino @petersutter can you take care of adding a test?

[rfranzke]

From https://github.com/gardener/gardener/blob/master/docs/deployment/getting_started_locally.md#creating-a-shoot-cluster:

⚠️ Please note that in this setup shoot clusters are not accessible by default when you download the kubeconfig and try to communicate with them. The reason is that your host most probably cannot resolve the DNS names of the clusters since provider-local extension runs inside the KinD cluster (see this for more details). Hence, if you want to access the shoot cluster, you have to run the following command which will extend your /etc/hosts file with the required information to make the DNS names resolvable:

How would we overcome this as part of an e2e test?

[timebertt]

In the e2e test, we could workaround this simply looking up the external DNSRecord of the shoot and swap out the hostname in the kubeconfig with the resolved IP address.

[timebertt]

With #5649, shoots/adminkubeconfig was exposed to endusers.
I think, it would be good to add an e2e test for it accordingly.

[shafeeqes]

/assign