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.

README.md

@@ -6,7 +6,6 @@
     - `/network` - config for tailscale, and NixOS container with automatic vpn tunneling via PIA
     - `/pc` - config that a graphical desktop computer should have. Use `de.enable = true;` to enable everthing.
     - `/server` - config that creates new nixos services or extends existing ones to meet my needs
-    - `/ssh.nix` - all ssh public host and user keys for all `/machines`
 - `/machines` - all my NixOS machines along with their machine unique configuration for hardware and services
     - `/kexec` - a special machine for generating minimal kexec images. Does not import `/common`
 - `/secrets` - encrypted shared secrets unlocked through `/machines` ssh host keys