[JENKINS-76157] Restore autoconfigure when auth is not null

[Dohbedoh]

JENKINS-76157

Since fabric8io/kubernetes-client#6153, the behavior described to not use autoconfigure ONLY IF there is no auth provided is not respected anymore. If one specifies the Kubernetes URL https://kubernetes.default.svc.cluster.local/ the client is not autoconfigured and use to the default namespace.

• adding tests that would have passed with Kubernetes client api < 6.13.2
• set autoconfigure when auth is null

Testing done

• Spin up Jenkins in Kubernetes in a namespace other than default
• Configure a Kubernetes Cloud and set the Kubernetes URL to https://kubernetes.default.svc.cluster.local/
• Try to provision a Kubernetes agent using the cloud

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed