Move audio configuration into a service module

- Move audio configuration into a service module to make it easily
  usable by multiple hosts.
- Allow configuration of AirPlay 2 name.
- Don't set MQTT topic of Shairport-Sync (AirPlay 2) explictly. Defaults
  to hostname now.
- Don't set sound.enable anymore, since its not needed.

modules/services/audio/librespot.nix

@@ -0,0 +1,42 @@
+# Sources for this configuration:
+# - https://github.com/librespot-org/librespot
+# - https://github.com/librespot-org/librespot/wiki/Options
+# - https://github.com/librespot-org/librespot/wiki/Audio-Backends
+
+{ config, pkgs, lib, ... }:
+
+with lib;
+
+let
+
+  cfg = config.ccchh.services.audio;
+
+in
+
+{
+  config = mkIf cfg.enable {
+    systemd.services.spotify-connect-receiver = {
+      enable = true;
+      description = "Spotify Connect Receiver Using librespot";
+      unitConfig = {
+        Requires = [ "network-online.target" "pipewire.service" ];
+        After = [ "network-online.target" "pipewire.service" ];
+      };
+      serviceConfig = {
+        ExecStart = "${pkgs.librespot}/bin/librespot --name '${config.ccchh.services.audio.name}' --device-type speaker --bitrate 320 --enable-volume-normalisation --disable-audio-cache --disable-credential-cache --quiet";
+        User = "librespot";
+        Group = "librespot";
+      };
+      wantedBy = [ "multi-user.target" ];
+    };
+
+    users = {
+      users.librespot = {
+        isSystemUser = true;
+        group = "librespot";
+        extraGroups = [ "pipewire" ];
+      };
+      groups.librespot = { };
+    };
+  };
+}