Frontend: Add Duo Code Review Requests by Role

Proposal

Add the Duo Code Review Requests by Role chart from https://gitlab.com/gitlab-org/gitlab/-/issues/570320#duo-code-review-usage-analysis using a tiled StackedColumnChart visualization.

The following data is being added via Backend: Duo Code Review namespace-level metric... (#570987 - closed)

• reviewByAuthorCount
• reviewByNonAuthorCount

Implementation

• Create data source? (assuming after Frontend: Add Duo Code Review usage over time m... (#573979 - closed) we can just extend the data source)
• Add visualization template to GitLab Duo and SDLC trends dashboard
• Update documentation