gitlab: Update chart to 10.2.6 and disable bundled Prometheus.

The Prometheus deployment never ran (its PVC has no storage class), and
chart 10.2 changed its immutable selector, which blocked the upgrade.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Change-Id: Ic701fef0cbbdd6784a98abc1ff76754fb8d1c683
1 file changed