Enable GitLab cloud native charts

[pameladelgado]

To be updated.

• [x] Deploy GitLab by itself #515
• [x] Translate custom gitlab chart configurations to native charts #515
• [x] Deploy GitLab along-side and connected to a Renku deployment #515
• [x] Explore and define migration from existing deployments #2093
• [x] Adjust renku helm-charts #2094
• [ ] Adjust documentation as needed
• [ ] Test/tune deployment options we did not have before (could be done separately)

Useful references

• https://docs.gitlab.com/ee/administration/auth/oidc.html
• https://gitlab.com/gitlab-org/charts/gitlab/-/tree/master/
• https://docs.gitlab.com/charts/installation/migration/