Update file extra_sidekiq_processes.md

What does this MR do and why?

Replaces a link that should go to our Helm chart docs, but for some reason linked to the Helm chart configurations for our Production environment for GitLab.com.

Addresses: gitlab-com/gl-infra/delivery#19276 (closed)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.