Move to Symfony Flex

The structure changed completely.
Bundles are gone. Everything is flatten in the folder `src`.
I separated import & api controllers to avoid _pollution_ in the main controller folder.

config/routes/scheb_2fa.yaml

@@ -0,0 +1,7 @@
+2fa_login:
+    path: /2fa
+    defaults:
+        _controller: "scheb_two_factor.form_controller::form"
+
+2fa_login_check:
+    path: /2fa_check