Add Metrics Dashboard embed pipeline to FF

What does this MR do and why?

This MR gates the metrics dashboard embeds pipeline functionality behind the remove_monitor_metrics feature flag. Frontend is done, but we also want to deprecate/remove any API-only access.

Related issue: Metrics: Delete GFM pipeline logic for embeds (#397137 - closed), (one of many MRs)

Context for removal:

• The Metrics Dashboard feature is being removed in %16.0.
  • Feature docs: https://docs.gitlab.com/ee/operations/metrics
  • Removal issue: Monitor: Metrics Deprecation and Removal (&10107), Remove Embed Grafana panels in Markdown (#389477 - closed)
• Most of the metrics dashboard frontend is currently behind the remove_monitor_metrics flag, but the flag has not yet been enabled. It needs to be enabled by default in time for %16.0.
  • The entire frontend should be behind the flag in order to enable it by default, but the API can merge after - as long as we make all breaking changes within %16.0.
  • Rollout issue: [Feature flag] Rollout of `remove_monitor_metrics` (#399248)
  • Tracking issue: Metrics: hide deprecated modules behind a featu... (#399231 - closed)
  • Enable-by-default MR: Set remove_monitor_metrics flag to true (!119989 - merged)

All related backend MRs to flag all metrics dashboard endpoints

• Add Metrics Dashboard annnotations API to FF (!120286 - merged)
• Add Metrics Dashboard starred dashboard API to FF (!120288 - merged)
• Add Metrics Dashboard templates viewer to FF (!120289 - merged)
• Add Metrics Dashboard environments API to FF (!120299 - merged)
• Add Metrics Dashboard settings API to FF (!120305 - merged)
• Add Metrics Dashboard GraphQL alert queries to FF (!120307 - merged)
• Add Metrics Dashboard embed pipeline to FF (!120310 - merged)
• Add Metrics Dashboard for internal dashboard en... (!120313 - merged)
• Add Metrics Dashboard base API to FF (!120316 - merged)

How to set up and validate locally

** pre-req: project with an environment

operation	how to test	before	after
Environment metrics embed	Pre-req: project with an environment FactoryBot.create(:environment) generate the appropriate url Gitlab::Routing.url_helpers .metrics_dashboard_project_environment_url( Environment.last.project, Environment.last, embedded: true ) Paste the url into a markdown field -> http://gdk.test:3000/namespace1/project-1/-/environments/1/metrics_dashboard?embedded=true Open dev tools & navigate to the Network tab Preview the markdown Note: edit the markdown after swapping the flag to reset the cached version	The metrics-related error is because of the frontend finding the dashboard & attempting to retrieve data. But my local env doesn't actually have a prometheus server returning data, so we just get an error	There's no error because we're not including a placeholder embed for the frontend to latch onto
Cluster metrics embed	Pre-req: project with a cluster ```ruby FactoryBot.create(:cluster, projects: [Environment.last.project], user: User.last) ``` \ 1. Same as the previous one! Gitlab::Routing.url_helpers .project_cluster_url( Environment.last.project, Clusters::Cluster.last, group: 'Group', title: 'Title', y_label: 'label' )
Alert metrics embed	Pre-req: alert --> See !120307 (merged) for setup instructions 1. Same as previous. Gitlab::Routing.url_helpers .metrics_dashboard_project_prometheus_alert_url( Environment.last.project, AlertManagement::Alert.last )
Grafana metrics embed	Pre-req: grafana integration FactoryBot.create(:grafana_integration, project: Environment.last.project) One more time! GrafanaIntegration.last.grafana_url + '/d/XDaNK6amz'

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.