Document and test email aliases

[leenaars]

While testing nixcloud-webservices I noticed that nixcloud mail documentation mentions the possibility of aliases but does not actually tell you how to create an alias.

[leenaars]

Note that if people read nix they can look at modules/services/email/virtual-mail-submodule.nix but normal users should not have to dig into source...

Note that the default config seems to result in an alias_database = hash:/etc/aliases which does not exist?

[qknight]

you are right