Use kubectl image digest with throttling fix

Summary

Uses the kubectl image digest with HOME=/tmp/kube, fixing the throttled commands that were causing timeouts and failures.

This change was picked into 5-9-stable with gitlab-org/charts/gitlab!2508 (merged).

Once all chart versions are at 5.9.4 and above, we can remove this override (see #682 (closed)).

Closes #625 (closed)

Closes #663 (closed)

Testing

Pipeline passed without requiring any manual retries of the review_* jobs.