Should be pure refactoring

This is my latest version of this, updated to work with the
packages in NixOS 21.05.

Grafana 8 on NixOS 21.11 fails harder than 7.x on 21.05 when its
`grafana-admin.password` file is missing.  Provide it regardless
whether Google auth is configured or not.

The Blackbox exporter can be used to check whether some services do answer;
We'll use it for our HTTPS endpoints.
Especially handy is it's checking for TLS cert expiry.

This lets other modules override these settings.

This should let it work for both enabled and disabled configurations

Fewer lines almost always better.  Also, we don't want to spread
these out unless we have to.

... we'll need this later for the TLS cert.

Also add my key to local secrets for the moment because otherwise localdev
grid cannot build itself :/