Draft: Add CI_KUBERNETES_ACTIVE for CI/CD tunnel

What does this MR do and why?

Sets CI_KUBERNETES_ACTIVE to 'true' when a CI/CD tunnel's KUBECONFIG is injected.

This variable is used by Auto Deploy to determine if deployments to Kubernetes clusters are expected.

The alternative would be to update all of the Auto DevOps Kubernetes jobs to also run if a KUBECONFIG is present:

   rules:
-    - if: '$CI_KUBERNETES_ACTIVE == null || $CI_KUBERNETES_ACTIVE == ""'
+    - if: '($CI_KUBERNETES_ACTIVE == null || $CI_KUBERNETES_ACTIVE == "") && ($KUBECONFIG == null || $KUBECONFIG == "")'
       when: never

Part of #299350 (closed)

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