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 too. @jacobvosmaer-gitlab make this easier updating the Gitlab::Redis class !6472 (merged)

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Why was this MR needed?

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Does this MR meet the acceptance criteria?

What are the relevant issue numbers?

Closes #22364 (closed)

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