♻️(serializers) move dimail calls to serializers

we move all business logic from model to serializer.
all API calls (direct and from front) will keep on triggering
expected 3rd party calls while admin actions will uniquely trigger
modifications in our database.

src/backend/mailbox_manager/utils/dimail.py

@@ -64,15 +64,15 @@ class DimailAPIClient:
         """Send a CREATE mailbox request to mail provisioning API."""
 
         payload = {
-            "givenName": mailbox.first_name,
-            "surName": mailbox.last_name,
-            "displayName": f"{mailbox.first_name} {mailbox.last_name}",
+            "givenName": mailbox["first_name"],
+            "surName": mailbox["last_name"],
+            "displayName": f"{mailbox['first_name']} {mailbox['last_name']}",
         }
         headers = self.get_headers()
 
         try:
             response = session.post(
-                f"{self.API_URL}/domains/{mailbox.domain}/mailboxes/{mailbox.local_part}/",
+                f"{self.API_URL}/domains/{mailbox['domain']}/mailboxes/{mailbox['local_part']}/",
                 json=payload,
                 headers=headers,
                 verify=True,
@@ -93,7 +93,7 @@ class DimailAPIClient:
             # In the meantime, we log mailbox info (including password !)
             logger.info(
                 "Mailbox successfully created on domain %s",
-                mailbox.domain.name,
+                str(mailbox["domain"]),
                 extra=extra,
             )
             return response