Enable feature flag default on

What does this MR do and why?

Describe in detail what your merge request does and why.

Turn feature flag show_relevant_approval_rule_approvers to be default on

Screenshots or screen recordings

Not applicable

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.

Related to #329153 (closed)