Follow-up from "doc: Add ClickHouse for GitLab.com readiness review"

The following discussion from !112 (merged) should be addressed:

• @mwasilewski-gitlab started a discussion: (+2 comments)

  Looking at the CHProxy repo it doesn't seem to have a connection pool or a query queue as features. Is that correct? Do we know at this point if these will be provided anywhere in our system?

  I see there's some rate limiting capability in CHProxy, is it going to be used? Or are rate limits going to be implemented somewhere else?