Support Grafana Chart

This first iteration for #1159 (closed)

1. Installs the Grafana chart
2. Configures the Prometheus data source
3. Imports the Omnibus GitLab dashboards
4. Creates & configures a random password to be used by Grafana
5. Adds an Ingress to expose Grafana at gitlab.tld/-/grafana

TODO:

• Automatically set the admin user/password with a secret
  • Add to shared-secrets to create a password secret for Grafana (easy)
  • Add grafana.admin.existingSecret (problem: static string property)
• Proxy all /-/grafana requests to this container
  • Add entry to Unicorn's Ingress

Future Iterations:

• Use globals for Grafana settings/configuration (upstream needs preparations)
• Use template(s) for key properties (upstream needs preparations) #1531 #1524
• Authenticate via GitLab using OAuth (upstream needs preparations)
• Document resource consumption (Expected CPU & memory resources within our environment, not just upstream suggestions)

Closes #1159 (closed)