Release Pipeline execution polices as an experiment

What does this MR do and why?

This MR releases the Pipeline execution policy feature as an experiment. We have added an experiment toggle in !138484 (merged).

Feature flag rollout issue: #424185 (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.