Versioning the pure JSON files representing the Grafana dashboards
had some disadvantages. It was hard to review them, they were very
cluttered and a lot was duplicated.
There are some tools that deal with that. One of them is Grafonnet,
which is a superset of Jsonnet, a tool to create JSON files using a
domain specific language.
This change implements the Gerrit Process dashboard in Grafonnet.
It also extends the installer to be able to install dashboards in
the Jsonnet format.
Change-Id: I6235fb7d045bd71557678a4e3b0d4ad4515f4615
