add KOPS_CL2_TEST_CONFIG to scalibility/run-test.sh

[alaypatel07]

This PR allows configuring custom test config file for invoking ClusterLoader2 scale tests.

It will be used here: kubernetes/test-infra#35699

[k8s-ci-robot]

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[alaypatel07]

cc @upodroid

[hakman]

/test pull-kops-e2e-k8s-gce-ipalias

[upodroid]

I added the DRA changes to #17671
/close

[k8s-ci-robot]

@upodroid: Closed this PR.

In response to this:

I added the DRA changes to #17671
/close

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