Auto-configure prefix-cache-scorer parameters from engine metrics

[learner0810]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Auto-configure prefix-cache-scorer parameters from engine metrics

Which issue(s) this PR fixes:

Fixes # partial fix: #1512

Does this PR introduce a user-facing change?:

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[k8s-ci-robot]

Hi @learner0810. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[ahg-g]

/assign @liu-cong
/ok-to-test

[ahg-g]

@learner0810 do we have a similar metric in sglang?

[learner0810]

@learner0810 do we have a similar metric in sglang?

I looked up the sglang documentation and didn't find it, so it probably isn't there yet.

[learner0810]

cc @liu-cong PTAL

[liu-cong]

do you plan to add the cache size metric as well? maybe in a follow up PR? That's a much more useful metric than the block size. In fact, the block size doesn't necessarily need to be the same with vllm

[learner0810]

Yes, If IGW requires cache size metric, I'd be happy to add that in a subsequent pull request.

[liu-cong]

cc @elevran

What's the status of the pluggable data layer? Can we use that to retrieve this new metric(s)?