Allow to configure IP-rate-limits in Omnibus/CNG
Follow-up from https://gitlab.com/gitlab-org/gitlab-pages/-/issues/490
- Add flags support to omnibus -> 1 MR
- Add flags to CNG -> 1 MR
- Add documentation to admin guide -> 1 MR
Follow-up from https://gitlab.com/gitlab-org/gitlab-pages/-/issues/490