web ui: New setting for browser-based login

This is useful in cases where OIDC login is active
which would then redirect the user to a central
login page.

See https://github.com/Kozea/Radicale/issues/2143

radicale/web/internal_data/js/config.js

@@ -0,0 +1,3 @@
+// This file is dynamically overwritten during serving. The contents here are just to enable development an testing.
+
+export const PREFER_BROWSER_LOGIN = false;