Add rate limiting for anonymous traffic to Projects List API endpoint

We want to rate limit the Projects List API endpoint. It is heavily used by the anonymous users - which affects our error budget.

We want to use this mechanism: https://gitlab.com/gitlab-org/gitlab/blob/6865b1dae1da1e34b792b2cb81dfbc68033609fe/lib/gitlab/application_rate_limiter.rb#L8

With application setting added, rate limiting should be easy to add. However, to be on the safe side we may want to feature flag it.