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.

machines/storage/s0/properties.nix

@@ -0,0 +1,20 @@
+{
+  hostNames = [
+    "s0"
+  ];
+
+  arch = "x86_64-linux";
+
+  systemRoles = [
+    "storage"
+    "server"
+    "pia"
+  ];
+
+  hostKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIAwiXcUFtAvZCayhu4+AIcF+Ktrdgv9ee/mXSIhJbp4q";
+
+  remoteUnlock = {
+    hostKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFNiceeFMos5ZXcYem4yFxh8PiZNNnuvhlyLbQLrgIZH";
+    onionHost = "r3zvf7f2ppaeithzswigma46pajt3hqytmkg3rshgknbl3jbni455fqd.onion";
+  };
+}