Extract multikueue integration tests to a dedicated CI job

[mimowo]

What would you like to be cleaned:

I would like to extract the integration multikueue tests to a dedicated suite.

Why is this needed:

The multikueue integration tests are quite heavy in nature, because:

• we run 3 instances of Kueue to simulate execution of 3 clusters (see here)
• we install opt-in CRDs to test MultiKueue with different frameworks (see here)
• they run INTEGRATION_NPROC=4 as other "lightweight" integration tests

For the experiments in the context of Kuberay multikueue integrations tests we learned that:

• increasing resources for the job for integration tests helped a little bit, but didn't fully solve the problem with running Ray (see comment)
• we know that setting INTEGRATION_NPROC=3 makes the tests usually pass, but it means lower parallelism enforced on the lightweight tests, which is not ideal

Another argument for the separate CI job is that the integration tests take long (around 18 min currently): https://prow.k8s.io/job-history/gs/kubernetes-ci-logs/logs/periodic-kueue-test-integration-main.

The MK integration tests take around 1min 50s of the time, so we could offload the main integration suite and allow for lower parallelism on the MK suite.

[mimowo]

cc @mszadkow @mbobrovskyi
WDYT @tenzen-y ?

[mszadkow]

/assign