feat: add labels to notebook statefulset

[monotek]

What:

• Add labels to statefulset created by notebook controller
• Same labels as for the pods are used

Why:

• It's best practice to have labels on all resources
• Be able to exclude statefulset from certain cluster policies (kyverno, opa) by label

[google-oss-prow]

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[kimwnasptd]

Thank you for the PR @monotek! For now we are in the process of having a first release for Notebooks V1.

Once this is out of the way we'll go to reviewing other PRs for V1. Although it's a bit under discussion on what further features/fixes we will be having on the V1 branch, and its support window, considering that there are significant efforts to finalise the V2 release.

[monotek]

Thanks for the update :)
Just let me know if I should add this PR to v2 as well.