Switch kubernetes:active with checking $KUBECONFIG

What does this MR do?

We have found an issue with kubernetes:active where it doesn't work with multiple clusters. Switch with the similar $KUBECONFIG variable check but this check actually gets the variable from the cluster matching the environment name.

What are the relevant issue numbers?

Fixes gitlab-ee#8311

Screenshots

Working AutoDevops (with the fix above) : https://gitlab.com/danielgruesso/support-test/pipelines/35844247

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [-] Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• [-] Conforms to the style guides
• [-] Conforms to the database guides
• [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.