Make Sympa + payment support optional

Signed-off-by: Emmy D'Anello <emmy.danello@animath.fr>

registration/management/commands/remind_payments.py

@@ -1,6 +1,7 @@
 # Copyright (C) 2024 by Animath
 # SPDX-License-Identifier: GPL-3.0-or-later
 
+from django.conf import settings
 from django.core.management import BaseCommand
 
 from ...models import Payment
@@ -13,5 +14,8 @@ class Command(BaseCommand):
     help = "Envoie un mail de rappel à toustes les participant⋅es qui n'ont pas encore payé ou déclaré de paiement."
 
     def handle(self, *args, **options):
+        if not settings.PAYMENT_MANAGEMENT:
+            return
+
         for payment in Payment.objects.filter(valid=False).filter(registrations__team__participation__valid=True).all():
             payment.send_remind_mail()