ICSTI-29: Add Grafana and predefined dashboards to K8S templates

As described in ICSTI-29 we would like to add grafana to the C2MON k8s cluster.

As part of this PR the following have happened:

• A C2MON Grafana image has been created and hosted on dockerhub
• A C2MON Grafana maven module has been created under c2mon-server/distribution/images/grafana containing some of our
• A data source has been configured in Grafana to point to the MySQL instance hosted in the C2MON k8s cluster
• A dashboard has been configured in Grafana with some basic insight into the data gathered by the Hostmetrics DAQ
• Both the data source and the dashboard are loaded into Grafana on startup
• Documentation has been updated to describe how to access Grafana in-cluster

Pending:

• Get the c2mon grafana image hosted in the cern dockerhub
• Once that's done, update the grafana yaml
• Consider adding more dashboards
• Consider adding default user with different password

Closes #256