Add descriptions to analytics dashboards

Problem to solve

Most of the dashboards listed under Analyze don't have descriptions.

Add/update descriptions to all analytics dashboards for a consistent style.

Dashboard	Current description	New description
Value Stream Analytics	-	Configure value streams for different stages of the DevOps lifecycle and visualize performance over time. Learn more.
Contributor analytics	-	Get insights into the commits made by projects members to a project over time. Learn more.
CI/CD analytics	-	Get insights into the performance and success rate of pipelines run in a project. Learn more.
Repository analytics	-	View the distribution of programming languages, code coverage, and commit statistics for a project/group. Learn more.
Code review analytics	Review time is the amount of time since the first comment in a merge request.	View metrics for merge requests in review and evaluate the code review process. Learn more.
Merge request analytics	Get insights into your merge request lifecycle and view trends over time.	-
Issue analytics	-	View metrics for the issues created in a group/project every month. Learn more.
Insights	Configure a custom report for insights into your group processes such as amount of issues, bugs, and merge requests per month. How do I configure an insights report?	Configure a custom report for insights into your group processes, such as number of issues, bugs, or merge requests per month. Learn more.
Value Streams Dashboard	Track key DevSecOps metrics throughout the development lifecycle. Learn more.	-
Duo and SDLC Trends	Visualize Duo usage and development trends side-by-side. Learn more about Duo and SDLC trends and Duo seats.	-