Add unmaintained notice to contrib spark

[annajung]

Signed-off-by: Anna Jung (VMware) [email protected]

Which issue is resolved by this Pull Request:
Part of #2311

Description of your changes:
Add README to /contrib/spark to mark the directory as unmaintained and out of date

Note:
Tagging spark component owners @Jeffwan @holdenk to ensure awareness of the out-of-date label on the component.

To remove the unmaintained label, check out the missing requirements #2311 and leave a comment on the issue to indicate that you'll take action to provide the missing requirements and are willing to keep the component up to date.

cc @kimwnasptd @kubeflow/wg-manifests-leads

[holdenk]

/approve +1 no longer maintaned

[annajung]

cc @kimwnasptd can you take a look? with @holdenk's approval, I think we can get this merged.

[annajung]

@kimwnasptd looking for your review! thanks

[kimwnasptd]

Apologies for the delay, looks good! Also, thank you for your time on this @holdenk. Hopefully, in the future, we can get a more solid integration story around Kubeflow and Spark and contributors to help maintain it.

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: annajung, holdenk, kimwnasptd

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