Track current concurrency limit in Redis

What does this MR do and why?

Concurrency limit is currently statically defined in Gitlab::SidekiqMiddleware::ConcurrencyLimit::WorkersMap based on concurrency_limit attribute (example)

With this change, we're adding a dynamic limit (current_limit) overriding the static limit tracked in Redis, which will be subject to throttling.

This currently does not affect any behavior in Sidekiq, it only changes from reading the limit from hardcoded value vs on Redis.

References

gitlab-com/gl-infra/data-access/durability/team#146 (closed)

Broken down from sidekiq throttling PoC !190565 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

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