feat: add mastodon module

modules/mastodon/options.nix

@@ -0,0 +1,42 @@
+{ config, lib, ... }:
+{
+  imports = [ ../options.nix ];
+
+  options.aether = {
+    mastodon = {
+      subdomain = lib.mkOption {
+        type = lib.types.nullOr lib.types.str;
+        default = "mastodon";
+        description = ''
+          The subdomain to host Mastodon under.
+
+          If null, then Mastodon is hosted at the domain itself.
+        '';
+      };
+
+      user = lib.mkOption {
+        type = lib.types.str;
+        default = "mastodon";
+        description = ''
+          The user to run Mastodon with.
+        '';
+      };
+
+      createUser = lib.mkOption {
+        type = lib.types.bool;
+        default = true;
+        description = ''
+          Whether to create the Mastodon user automatically.
+        '';
+      };
+
+      email = lib.mkOption {
+        type = lib.types.str;
+        default = config.aether.acmeEmail;
+        description = ''
+          The email address used by Mastodon to send emails from.
+        '';
+      };
+    };
+  };
+}