MR Analytics: Navigation

Problem to solve

We want to introduce a Throughput chart on a new "Merge Request Analytics" page. However, first that page needs to exist.

Proposal

There should be a project-level "Merge Request Analytics" page, behind a feature flag, accessible from the group-level left-nav.

Out of scope

Content will be added to this new page in future iterations (like Throughput and MTTM).

Additional information

The feature flag is called project_merge_request_analytics and this feature is being implemented in !38139 (merged)