Use a ConnectionPool for Rails.cache on Sidekiq servers
## What does this MR do?
On Sidekiq server we'll use a connection pool to connect to the redis store used for Rails cache. But now we're sure we're not modifying the configuration used on the lazy create Redis connection inside the connection pools. I've create a PR on [redis-activesupport](https://github.com/pacoguzman/redis-activesupport) too. @jacobvosmaer-gitlab make this easier updating the Gitlab::Redis class !6472Closes#22364
See merge request !6468
ce0591df70