Extend helm chart to optionally include grafana dashboards

[jcpunk]

It would be nice if the helm chart had a boolean flag to optionally include the example grafana dashboards. Something similar to what is used in kube-prometheus-stack, strimzi operator, and cilium would be ideal.

[benjaminjb]

Same questions as #201

Oh, perhaps it would help to know that we have a Helm chart for our monitoring stack, which you can get at oci://registry.developers.crunchydata.com/crunchydata/crunchy-monitoring