requested to merge 18663-perform-housekeeping-with-proper-connection-pool-size into master
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
This MR configure Gitlab::Redis to use a pool with a size related with the number of threads running the current process.
Are there any race condition setting the pool class instance variable?
master (if you do - rebase it please)
Relates #18663 (moved)