feat: Introduce cache_key for cache key customization

[zzmao]

Description of your changes:
Introduce cache_key for cache key customization for issue #11328
Doc: https://docs.google.com/document/d/1oNgYyFYondaVSFf9Pd3Q9uVzaqBr5wrOMHKgX9MMa78/edit?tab=t.0

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[chensun]

/lgtm
/approve

[google-oss-prow]

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[HumairAK]

Thanks @zzmao !

This is spawning from https://docs.google.com/document/d/1oNgYyFYondaVSFf9Pd3Q9uVzaqBr5wrOMHKgX9MMa78/edit?tab=t.0 right? @zzmao can we get an associated github issue for this and mention both the doc and the issue in the PR body for tracking purposes?

is there a backend follow up planned for this pr?

You'll also need to sign off on your commits to pass the dco check

[google-oss-prow]

New changes are detected. LGTM label has been removed.

[zzmao]

Hi @HumairAK ,

Thanks for the review. Addressed your comment.

Backend change is TBD. Open for community contribution.