Rate-limit unauthenticated wiki reads

What does this MR do and why?

Rate-limits unauthenticated wiki reads, counted per project or group wiki, under a new FF, wiki_read_unauthenticated_rate_limit.

The limit is an application setting, wiki_read_request_limit_unauthenticated, set to 500/min by default.

The FF is checked against the wiki's project or group.

References

• https://gitlab.com/gitlab-org/gitlab/-/work_items/635643+ (staff-only)

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.