Frontend: Duo Code Review comment sentiment

Proposal

Add the Code Review comment sentiment chart from https://gitlab.com/gitlab-org/gitlab/-/issues/570320#duo-code-review-usage-analysis using a LineChart visualization. Display two series showing 👍 and 👎 rates calculated as percentages of postCommentCount (thumbsUpCount / postCommentCount and thumbsDownCount / postCommentCount).

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

• postCommentCount
• thumbsUpCount
• thumbsDownCount

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

Alternative metrics that might be more valuable:

Related to comment #574005 (comment 2879468202) it would be more reliable to focus on behavioral metrics:

• Suggestion application rate: How often are Duo's suggestions actually applied to the code?
• Time to merge after Duo review: Does Duo accelerate the review cycle?
• Response engagement: Do authors respond to Duo comments (regardless of emoji)?
• Review completion rate: When Duo is assigned, how often does the MR successfully merge?