Merge branch '430975-cached-messages' into 'master'

ChatStorage: memoize messages, add find_previous_from

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/138280



Merged-by: Pavel Shutsin <pshutsin@gitlab.com>
Approved-by: Pavel Shutsin <pshutsin@gitlab.com>
Reviewed-by: Mark Chao <mchao@gitlab.com>
Reviewed-by: Pavel Shutsin <pshutsin@gitlab.com>
Co-authored-by: Mark Chao <mchao@gitlab.com>