Investigate build process for Grafana versions post-phantomjs removal

[isaacdavis]

The Triton Grafana service uses Joyent's fork of Grafana. The sole difference between the fork and the upstream repo is that the fork removes phantomjs from the build, since phantomjs won't build on illumos.

With the release of Grafana 7.0, phantomjs has been removed from the upstream Grafana repo entirely and replaced with a new image rendering plugin using headless chromium.

Thus, if this repo is upgraded to use a version of Grafana >= 7.0, we will probably have to update the content and build process of the Grafana fork. It would be nice if we no longer need a fork at all, but I have a hunch that chromium on illumos will prove problematic as well.