VSA: Add last_approved_at event

Release note

Enhancing Workflow Visibility: New Insights into Merge Request Review Time

To improve development workflow tracking, GitLab’s Value Stream Analytics has been extended with a new event: last_approved_at. This event marks the end of the review phase and the start of the final pipeline run or merge stage. For example, you can create a VSA stage with last_approved_at as the start event and reviewer_first_assigned as the end event to calculate total merge request review time. Reducing the review time directly impacts the overall cycle time of development, leading to faster software delivery.

Problem

We currently don't have an accurate way to determine the MR review time ion VSA. We have reviewer first assigned but no event to signify the end of review and the beginning of the final pipeline run / merge stage.

Context from VSA: tracking MR review iterations (#499757)

Proposal

Add a last_approved_at event to the MR type which can be used in conjunction with reviewer first assigned to calculate the total merge request review time.

Implementation details:

• Update Cycle Analytics under cycle_analytics/stage_events