feat: enable custom_reg_form capability

Enable the custom_reg_form.
The field could be used using the `REGISTRATION_EXTENSION_FORM` dict  setting
https://github.com/openedx/edx-platform/blob/master/openedx/core/djangoapps/user_authn/views/register.py#L205

refs: #253

eox_core/edxapp_wrapper/backends/users_m_v1.py

@@ -39,6 +39,7 @@
     REGISTER_USER as post_register  # pylint: disable=import-error
 from openedx.core.djangoapps.user_authn.views.registration_form import (  # pylint: disable=import-error
     AccountCreationForm,
+    get_registration_extension_form,
 )
 from openedx.core.djangolib.oauth2_retirement_utils import \
     retire_dot_oauth2_models  # pylint: disable=import-error,unused-import
@@ -174,12 +175,12 @@ def create_edxapp_user(*args, **kwargs):
 
     # Go ahead and create the new user
     with transaction.atomic():
-        # In theory is possible to extend the registration form with a custom app
+        # Is possible to extend the registration form with a custom app
         # An example form app for this can be found at http://github.com/open-craft/custom-form-app
-        # form = get_registration_extension_form(data=params)
+        custom_form = get_registration_extension_form(data=account_creation_form_data["data"])
         # if not form:
         form = EdnxAccountCreationForm(**account_creation_form_data)
-        (user, profile, registration) = do_create_account(form)  # pylint: disable=unused-variable
+        (user, profile, registration) = do_create_account(form, custom_form)  # pylint: disable=unused-variable
 
     site = kwargs.pop("site", False)
     if site: