Add configuration sanity check dashboard

We've seen that, if either the Exporter or cbmultimanager are misconfigured, Grafana can break in hard to troubleshoot ways. Would be good to add a dashboard that runs a set of "sanity check" queries against all of them and shows their results in an easy to understand way.

Perhaps we can then link to it as the last step in the installation guide (i.e. "go here to check you've done it all properly")