Add danger error comment when altering sidekiq arguments

What does this MR do and why?

Adds a danger rule to warn MR authors when adding a new sidekiq argument that there is a process to follow that covers multiple milestones.

This was a corrective action after a recent feature flag rollout caused a production incident.

Screenshots or screen recordings

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.

Mentions #362192 (closed)