Pull in mature schema for Grafana dashboards, plugins

[sdboyer]

To get to the point where we can make minimal use of polly, we absolutely have to have sufficiently mature schema for all of our key object types. Prometheus is good enough - thankfully, rules and alerts aren't complicated - but Grafana dashboards are, of course, the hard one.

We're pushing hard on getting this done (now that everyone's back from summertime vacations). Issue to track it is here: grafana/grafana#36844

[sdboyer]

The referenced upstream issue is now complete! (big yaaaay! took a lot of effort.) That leaves two bits for us:

• Copying in the updated schema (easy, done in Copy over new and updated Grafana schema #32)
• Doing the logical composition of those plugin schema into the core dashboard schema

The latter is something that really properly needs to be done with an improved scuemata system, which is ~next on my priority list now that the schema themselves are updated. But i think i can hack something together as a one-off that'll work for now.

[sdboyer]

More detailed description of what "doing the logical composition..." means in #34 (comment)