add send mail lib

server-api/config.json.default

@@ -16,5 +16,13 @@
             "port": 27017,
             "dbname": "lora"
         }
+    },
+    "smtp": {
+        "sys_mail": "admin@localhost",
+        "host": "localhost",
+        "port": 587,
+        "secure": false,
+        "user": "admin",
+        "pass": "pass"
     }
 }