Merge branch 'ck3g-add-info-about-metrics_dashboard-feature-flag' into 'master'

Fill in info for metrics_dashboard feature flag

See merge request gitlab-org/gitlab!43591

config/feature_flags/development/metrics_dashboard.yml

 ---
 name: metrics_dashboard
-introduced_by_url: 
-rollout_issue_url: 
-group: 
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/29634
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/257902
+group: group::health
 type: development
 default_enabled: true