Just require hostName and domain instead of an extra publicIPv4 option.  Leave
behind a similar option, `publicAddress`, just in case it needs to be
overridden at some point, but stop supplying a value for it anywhere.

Put its contents in it and then use them from there instead of importing them
all over the rest of the code.

Also change the `domain` parameter for Grafana to always
use that beautiful name - besides display it's cosmetic anyway
IIANM so I'll not parametrize it for now.

For consistency reasons: Even if they had a perfectly good swap
partition already, and also for AWS hosts.

See https://whetstone.privatestorage.io/privatestorage/PrivateStorageio/-/merge_requests/103#note_13854

The original domain got some state created for it by certbot.  The
certificates are anchored to `payments.privatestorage.io` in the filesystem.
The code handling these domains uses the first domain name in the list to find
the certificates, so make it match the filesystem state.

More flexibility and less dots in config files.
Implements #65.

We might want to merge this before turning on live payment.

Related to privatestorageops#333.

Discern make-issuer.nix from issuer.nix better.