nixos/lemmy: support nginx

[uninsane]

Description of changes

allows users to deploy lemmy as a nginx virtual host. for example:

{
  services.lemmy = {
    enable = true;
    settings.hostname = "lemmy.mydomain.tld";
    # tell nginx to proxy the above hostname to lemmy
    nginx.enable = true;
  };
}

services.lemmy.nginx.enable aims to be equivalent to the existing services.lemmy.caddy.enable option.

for a complete lemmy/nginx deployment on NixOS, see:

• the nixos config
• a live deployment

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 23.05 Release Notes (or backporting 22.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

[happysalada]

I dont know nginx very well, but these changes look good to me. Im waiting 24h to give bill time to see these changes.

[icewind1991]

Tested with my local instance, all looks good

[happysalada]

@uninsane thank you! Feel free to ping me for any rust related tooling (in case you don't have someone in particular in mind for review).