[Docs] Document the implications of using a release name other than "gitlab"

Summary

Related to #545 (closed)

The manifests that we ship to install the Operator assume a name prefix on most objects of gitlab-.

That matches our documentation of the GitLab CR where we set metadata.name=gitlab.

However, if someone chooses a different release name, issues can arise like #545 (closed). The only workaround would be to modify the Operator manifest prior to installation, or only use gitlab as the release name.

Acceptance criteria

• (Research) List the objects that would need to be manually updated in the Operator manifest if using a different release name
• (Implementation) Document the objects that would need to be manually updated if using a different release name
• (Research/follow-up) Investigate a better way to handle this