Implement vcluster for ephemeral, isolated cluster testing

Summary

In gitlab-org/charts/gitlab#5013 (closed), we're doing a phased rollout of vcluster for ephemeral, isolated environments in our CI tests.

Based on the outcome of that change, and specifically gitlab-org/charts/gitlab#5013 (closed), let's implement a similar approach here in the Operator to take the same advantages.

Acceptance criteria

• gitlab-org/charts/gitlab#5013 (closed) is addressed
• Follow-up issue(s) created for Operator's implementation