GitLab Pages Source IP Rate Limiting

Follow-up 2 https://gitlab.com/gitlab-org/gitlab-pages/-/issues/490#note_676655191

• Add a ratelimit package with support for source IP rate limit
• Add middleware
• Add metrics

Release notes

GitLab Pages can become quite popular. When too many users are trying to access the Page at the same time, this can lead to an outage.

In this release, GitLab is introducing rate limiting per source IP. This will make Pages hosted on gitlab.com more stable. For users with a self hosted GitLab instance, you can also limit the number of concurrent requesters.