Add "Closed issues" metric to VSD comparison table

What does this MR do and why?

Introduces issues_completed count total to the Value Stream Dashboard for both groups and projects, as well as their respective queries (GroupValueStreamAnalyticsFlowMetrics.issuesCompletedCount and ProjectValueStreamAnalyticsFlowMetrics.issuesCompletedCount)

Screenshots or screen recordings

Before	After	After - limit tooltip

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Please make sure that you have a GitLab Ultimate license
2. Create a group
3. Seed cycle analytics data
4. Seed dora metrics data
5. Feature.enable(:vsd_graphql_dora_and_flow_metrics)
6. Visit the Value streams dashboard and verify that the Closed issues metric is present and working correctly

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #386715 (closed)