Grafana dashboard with Solr stats

[jachro]

As a renku system administrator, I'd like to have a Grafana dashboard showing some Solr metrics.

Acceptance criteria:

• Enable and configure the Solr chart in order to make the metrics available (there's a Metrics parameters section in https://artifacthub.io/packages/helm/bitnami/solr)
• Some Grafana dashboard with some relevant stats (as we don't exactly know what we'd like to see, it's down to the dev to decide what we put in the first iteration)
• Make sure a PR on the terraform-renku repo is created for the dashboard(s) (here's where they go: https://github.com/SwissDataScienceCenter/terraform-renku/tree/main/gitops/common/app/monitoring/grafana/dashboards)