Value Streams Dashboard: Add MR throughput to the "Metrics comparative table"

Release notes

MR throughput metrics in the Value Streams Dashboard

The Value Streams Dashboard has been enhanced with a new metrics - MR throughput. With this new metric users can identify Low or high productivity months and the efficiency and productivity of your merge request and code review processes.

Overview

Problem to solve

Proposal

Add the following DevOps metric to the comparative table:

1. MR Throughput: monthly number of merged merge requests. Trend color - green for increase.
2. permissions - Developer and above. All metrics are visible to anyone who has access to this page.
3. Data query with Project.mergeRequests and Group.mergeRequests graphql query which both return a MergeRequestConnection,
4. Add tooltips and drill-down links to the metrics names (description below).

Tooltips description:

Metric name	Description	Drill down for deeper insights	Go to Docs
MR Throughput	Monthly number of merged merge requests	https://gitlab.com/gitlab-org/gitlab/-/analytics/merge_request_analytics?start_date=2021-11-24&end_date=2022-11-24 (Last 180 days date range)	https://docs.gitlab.com/ee/user/analytics/merge_request_analytics.html#mean-time-to-merge

Acceptance criteria

Compare the metrics between these projects in one view:

1. GitLab.org / GitLab FOSS
2. GitLab.org / GitLab
3. GitLab.org / GitLab Design
4. GitLab.org / GitLab Docs