Enable Grafana Enterprise

Current upstream Grafana does not currently provide a clear path to enabling Grafana enterprise and assumes you will manually create a configmap and configure the deployment to utilize it.

This issue is to streamline that configuration process for our chart users, but not require that the secret is managed by Big Bang.

• Add configurations to Umbrella to automatically configure Grafana Enterprise
• Create an optional secret template to handle auto-creation of the license file
• Create a docs/enterprise.md file that covers how to enable Grafana Enterprise