Metrics: hide deprecated modules behind a featureflag

When flag is enabled:

MR 1

• hide Monitor > Metrics view and left navigation item
• hide Settings > Monitor > Metrics
• hide Settings > Monitor > Grafana authentication
• hide Settings > Integrations > Prometheus > Metrics (project level)
• hide Settings > General > Visibility, project features, permissions > Monitor > Metrics Dashboard

MR 2

• hide Health tab from Infrastructure > Cluster

MR 3

• hide metrics embeds rendering

MR 4

• hide Settings > Integrations > Prometheus