Refactor imports and secrets. Add per system properties and role based secret access.

Highlights
- No need to update flake for every machine anymore, just add a properties.nix file.
- Roles are automatically generated from all machine configurations.
- Roles and their secrets automatically are grouped and show up in agenix secrets.nix
- Machines and their service configs may now query the properties of all machines.
- Machine configuration and secrets are now competely isolated into each machine's directory.
- Safety checks to ensure no mixing of luks unlocking secrets and hosts with primary ones.
- SSH pubkeys no longer centrally stored but instead per machine where the private key lies for better cleanup.

common/server/mailserver.nix

@@ -33,7 +33,7 @@ in
       inherit domains;
       loginAccounts = {
         "jeremy@runyan.org" = {
-          hashedPasswordFile = "/run/agenix/email-pw";
+          hashedPasswordFile = "/run/agenix/hashed-email-pw";
           # catchall for all domains
           aliases = map (domain: "@${domain}") domains;
         };
@@ -54,7 +54,7 @@ in
       ];
       certificateScheme = 3; # use let's encrypt for certs
     };
-    age.secrets.email-pw.file = ../../secrets/email-pw.age;
+    age.secrets.hashed-email-pw.file = ../../secrets/hashed-email-pw.age;
     age.secrets.hashed-robots-email-pw.file = ../../secrets/hashed-robots-email-pw.age;
 
     # sendmail to use xxx@domain instead of xxx@mail.domain