[feat] Add running requests scorer and tests

[BenjaminBraunDev]

This PR adds a running request scorer and tests, it's very similar to the queue scorer, but for the running requests metric added in #1899. It's weighted the same as queued requests in the default plugin config.

Does this PR introduce a user-facing change?:

NONE

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: BenjaminBraunDev
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[BenjaminBraunDev]

Removed the running request scorer from the config until we benchmark it's performance.

[k8s-ci-robot]

PR needs rebase.

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[k8s-ci-robot]

@BenjaminBraunDev: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-gateway-api-inference-extension-test-unit-main	11f4e05	link	true	/test pull-gateway-api-inference-extension-test-unit-main
pull-gateway-api-inference-extension-test-e2e-main	11f4e05	link	true	/test pull-gateway-api-inference-extension-test-e2e-main
pull-gateway-api-inference-extension-verify-main	11f4e05	link	true	/test pull-gateway-api-inference-extension-verify-main

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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