Refactor MX record structure in JSON

Updated MX record format to include target and priority.

domains/send.send.serchidev.json

@@ -4,7 +4,12 @@
     "email": "serchidev@gmail.com"
   },
   "records": {
-    "MX": ["10 feedback-smtp.eu-west-1.amazonses.com."],
+    "MX": [
+      {
+        "target": "feedback-smtp.eu-west-1.amazonses.com",
+        "priority": 10
+      }
+    ],
     "TXT": "v=spf1 include:amazonses.com ~all"
   }
 }