[EPIC] Create Plutono plugin

[artherd42]

Context

A platform like Greenhouse should have a tool for visualising dashboards. Currently Plutono is used as a solution, a fork of Grafana 7.5.17 under the Apache 2.0 licence, limited to maintenance and security updates.

Tasks

• ([plutono] Initialise the plugin with basic functionality  #273)

[richardtief]

The Grafana community helm chart has been transferred to Plutono. Checked out at appVersion: 7.5.3 as it is the last source before Grafana v8.

[auhlig]

As discussed with @richardtief via IM: Initially only in remote clusters with pre-configured datasource as part of kube-monitoring plugin.
Document how to provide custom dashboards.

@kengou to work on dashboards provided via [k8s-monitoring](https://github.com/cloudoperators/k8s-monitoring] repository.

More clarification needed on holistic plutono in central cluster. Related ADR#6

[auhlig]

Q3 deliverables:

• [Plutono] plugin available with basic functionality. See [plutono] Initialise the plugin with basic functionality  #273
• Integration with and auto-discovery of existing Prometheus data sources

[auhlig]

This is done, right @richardtief?

[richardtief]

Completed. New issues are created for subsequent functions.