🗃️(mailbox_manager) add organization to domain

To be able to provide a SIRET in the ProConnect IdP process
we need to be able to link a mail domain to its organization.
For now this is not mandatory, as we can't detect the organization
and need a frontend process to clarify it.

src/backend/mailbox_manager/models.py

@@ -8,7 +8,7 @@ from django.db import models
 from django.utils.text import slugify
 from django.utils.translation import gettext_lazy as _
 
-from core.models import BaseModel
+from core.models import BaseModel, Organization
 
 from mailbox_manager.enums import (
     MailboxStatusChoices,
@@ -23,6 +23,13 @@ class MailDomain(BaseModel):
     name = models.CharField(
         _("name"), max_length=150, null=False, blank=False, unique=True
     )
+    organization = models.ForeignKey(
+        Organization,
+        on_delete=models.PROTECT,
+        related_name="mail_domains",
+        null=True,
+        blank=True,
+    )
     slug = models.SlugField(null=False, blank=False, unique=True, max_length=80)
     status = models.CharField(
         max_length=20,