Add importable clan.modules and clan.template interfaces without implementation

lib/build-clan/templates/interface.nix

@@ -0,0 +1,28 @@
+{
+  lib,
+  ...
+}:
+let
+  types = lib.types;
+in
+{
+  options = {
+    # clan.templates.disko
+    disko = lib.mkOption {
+      type = types.attrsOf (types.submodule { imports = [ ./disko/interface.nix ]; });
+      default = { };
+      description = ''
+        Holds different disko templates.
+      '';
+    };
+
+    # clan.templates.clan
+    clan = lib.mkOption {
+      type = types.attrsOf (types.submodule { imports = [ ./clan/interface.nix ]; });
+      default = { };
+      description = ''
+        Holds the different clan templates.
+      '';
+    };
+  };
+}