Add Monitor :: Health metadata

Add this page to the docset for Monitor :: Health.

doc/raketasks/generate_sample_prometheus_data.md

 ---
-stage: none
-group: unassigned
+stage: Monitor
+group: Health
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
 ---