Merge branch 'if-368926-autocomplete_users_rate_limit_doc' into 'master'

Documentation for autocomplete users rate limit settings

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/184293



Merged-by: Imre Farkas <ifarkas@gitlab.com>
Approved-by: Isaac Durham <idurham@gitlab.com>
Reviewed-by: Isaac Durham <idurham@gitlab.com>