Run recommend_reviewers flow when a merge request is created

What does this merge request do and why?

Adds a merge request trigger with a created precondition to the Recommend Reviewers foundational flow, the same as the Risk Classification flow. When a group enables the flow, each project gets the trigger.

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

merge request acceptance checklist

Evaluate this merge request against the merge request acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.