Update Reference Architecture to follow Omnibus GitLab High Availability Roles after refactor

groupdistribution is working on gitlab-org&7300 to revamp and update existing roles. Once the work is done, Reference Architecture documentation would need to be updated to use latest roles and guidance.

• https://docs.gitlab.com/omnibus/roles/

Rollout process: documentation update should be done in batch for all updated roles in the next upgrade stop after the epic is close to allow for graceful switch period.