Add Grafana Dashboard Template

There is a grafana dashboard json file available upstream at the prometheus-elasticsearch-exporter repo, let's kpt pull that into a dashboards folder (next to chart/) and create necessary configMap template to conditionally insert the dashboard into the cluster for the monitoring package to pick up: https://repo1.dso.mil/platform-one/big-bang/apps/cluster-utilities/velero/-/merge_requests/55/diffs

• JSON file present in package
• configmap brought in to reference dashboard and relevant information
• Dashboard shows up and shows data within Grafana deployed alongside EK installation with metrics.enabled=true & monitoring.enabled=true