✨(domains) get domain expected config for DNS

Call dimail to get DNS configuration values
to make an external domain work and save it in our db.
Add values to serializer for displaying.

src/backend/mailbox_manager/utils/dimail.py

@@ -519,3 +519,48 @@ class DimailAPIClient:
             if isinstance(value, dict) and value.get("internal") is internal
         }
         return {key: value.get("ok", False) for key, value in checks.items()}
+
+    def fetch_domain_expected_config(self, domain):
+        """Send a request to dimail to get domain specification for DNS configuration."""
+        try:
+            response = session.get(
+                f"{self.API_URL}/domains/{domain.name}/spec/",
+                headers={"Authorization": f"Basic {self.API_CREDENTIALS}"},
+                verify=True,
+                timeout=10,
+            )
+        except requests.exceptions.ConnectionError as error:
+            logger.exception(
+                "Connection error while trying to reach %s.",
+                self.API_URL,
+                exc_info=error,
+            )
+            return []
+        if response.status_code == status.HTTP_200_OK:
+            # format the response to log an error if api response changed
+            try:
+                dimail_expected_config = [
+                    {
+                        "target": item["target"],
+                        "type": item["type"],
+                        "value": item["value"],
+                    }
+                    for item in response.json()
+                ]
+                domain.expected_config = dimail_expected_config
+                domain.save()
+                return dimail_expected_config
+            except KeyError as error:
+                logger.exception(
+                    "[DIMAIL] spec expected response format changed: %s",
+                    error,
+                )
+                return []
+        else:
+            logger.exception(
+                "[DIMAIL] unexpected error : %s %s",
+                response.status_code,
+                response.content,
+                exc_info=False,
+            )
+            return []