Documentation: Which Monitoring solution for predefined dashboards?

[stefanigel]

As a user who has subscribed for Stackable Support I want to use the predefined Grafana dashboards.. I need to know which Prometheus / Grafana Version to use, where to get the operator, how to get and install the dashboards.

TODO: Enhance monitoring documentation to cover the needs of the subscriber.

Acceptance criteria:

• it is described in the docs how to get and install the dashboards
• it is described which Prometheus / Grafana Stack has to be used to make use of the dashboards
• the doc can be referenced from our support subscription agreements