Add extended options for Owncloud remotes

lib/modules/rclone.nix

@@ -129,11 +129,29 @@ let
         };
       }));
 
+  mkOwncloudProvider = { displayName ? "Owncloud", vendor ? "owncloud" }: (
+    { config, ... }: {
+      imports = [
+        (mkWebdavProvider { inherit displayName vendor; })
+      ];
+
+      options = {
+        baseUrl = lib.mkOption {
+          type = lib.types.str;
+          description = "The base url of the ${displayName} server for automatically determining the WebDAV url.";
+        };
+      };
+
+      config = {
+        url = "${lib.strings.removeSuffix "/" (lib.strings.normalizePath config.baseUrl)}/remote.php/dav/files/${config.username}";
+      };
+    });
+
   syncProviders = {
     nextcloud = rec {
       displayName = "Nextcloud";
 
-      module = mkWebdavProvider {
+      module = mkOwncloudProvider {
         inherit displayName;
         vendor = "nextcloud";
       };