[receiver/k8scluster] e2e test

[dmitryax]

There is an e2e test for k8s attributes processor. We need to introduce similar tests for k8s cluster receiver and add it to the workflow. The common k8s utilities from the existing e2e test can be moved to a dedicated module in the contrib so it can be reused by the k8s cluster receiver as well.

[github-actions]

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