Import documentation from Documentation project

Summary

We currently have some documentation in https://gitlab.com/gitlab-org/gl-openshift/documentation.

That project is a bit outdated given recent work on the Operator, and it has been discussed a few times to migrate the docs in that project into the GitLab Operator project.

To do

• Merge documentation from Documentation project into GitLab Operator project (!120 (merged))
• Copy over resulting documentation from gitlab-org/gl-openshift/documentation!7 (merged)
• Delete (or archive) the Documentation project