Connector 2.0 first beta

Checkmk's Grafana connector underwent a complete rewrite and has now entered its Beta testing stage. This plugin release accompanies the upcoming checkmk 2.1 release, yet for testing purposes it will work with checkmk 2.0.0p20

An update script is available to migrate the configuration from the previous connector to this new one. However, there are some backwards incompatible changes and not all features are conserved.