Closes #143.
Thanks to http://nixos.wiki/wiki/Nix_Language:_Tips_%26_Tricks for
inspiration.

Thanks @bendon!

This reverts commit c8a13555.

Sadly, Borg says this is not a good idea: https://borgbackup.readthedocs.io/en/stable/faq.html#can-i-backup-from-multiple-servers-into-a-single-repository

Spoiler:  This won't work, Borg does not guarantee consistency with
parallel writers to the same repo as I now found out.

... and fix that option the other commit introduced

If I understand the behavior current Prometheus and Grafana
correctly, this should remove the port number from the
paymentserver labels in Prometheus TDSB.

Copy everything from how the issuer does it.

As per our discussion in PrivateStorage sync meeting today.

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