Removed hardcoded 1.31 version for `compatibility-versions-e2e.yaml` test and properly parameterize the n-1..3 release branch

[aaron-prindle]

Currently config/jobs/kubernetes/sig-testing/compatibility-versions-e2e.yaml has the hardcoded value:

     env:
      - name: EMULATED_VERSION
        value: "1.31"  # TODO(aaron-prindle) FIXME - hardcoded for now

For selecting the emulation version and currently in experiment/compatibility-versions/e2e-k8s-compatibility-versions.sh the k8s branch to clone is parameterized BUT not set in `compatibility-versions-e2e.yaml

  KUBE_RELEASE_BRANCH=${KUBE_RELEASE_BRANCH:-release-1.31}

This issue tracks properly parameterizing this. See related PR comment here: https://github.com/kubernetes/test-infra/pull/33534#discussion_r1785314623

which mentions that using https://github.com/kubernetes/test-infra/tree/master/releng/config-forker might be a good solution here

/assign @aaron-prindle

[aaron-prindle]

/sig api-machinery