Send payment confirmation mail after payment, and send weekly reminders for people that have not paid

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

registration/management/commands/remind_payments.py

@@ -0,0 +1,17 @@
+# Copyright (C) 2024 by Animath
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+from django.core.management import BaseCommand
+
+from registration.models import Payment
+
+
+class Command(BaseCommand):
+    """
+    This command sends a mail to each participant who has not yet paid.
+    """
+    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):
+        for payment in Payment.objects.filter(valid=False).filter(registrations__team__participation__valid=True).all():
+            payment.send_remind_mail()