Grafana dashboard box links are no longer valid in Grafana 8.4

This issue is separate from, but closely related to, NMS-14109.

Steps to reproduce:

1. Configure the Grafana box properties and switch on rendering of the box (see docs)
2. Create at least one dashboard in your connected Grafana instance
3. Restart OpenNMS and load the landing page

Expected result: Links from Grafana box take you to the dashboards named in the link text

Actual result: Links from Grafana box take you to a "dashboard not found" page in Grafana

I've poked around behind the curtain and think I've isolated the cause. When we build the links in the Grafana box, we assume that appending the uri property obtained for the dashboard in question on the end of the concatenation of the configured grafanaProtocol, grafanaHostname, grafanaPort, grafanaBasePath, and the constant "/dashboard/" will yield a valid URL. Evidently this used to work but broke somewhere along the way.

My poking also indicates that using the url property, concatenated with the protocol, host, and port, should make a valid URL.