Copy everything from how the issuer does it.

As per our discussion in PrivateStorage sync meeting today.

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.

Epiphany: Systemd reads more than a single environment file. This
lets me improve the file naming much.

Unfortunately still prints a bold warning on deployment.

This will store the supposedly secret URL in the Nix Store and
print a honking big warning about it.

This reduces the confusion with the nixos/modules/deployment.nix module,
and should make it clearer that it can contain any configuration that
applies to all hosts on the grid.

Using AWS is what causes it so using AWS can be what fixes it, too.

... This breaks the tie, thx to https://github.com/DBCDK/morph/issues/146