refactor: split iot models by entity

backend/api/internal/models/iot_migrate.go

@@ -0,0 +1,9 @@
+package models
+
+import "git.apinb.com/bsm-sdk/core/database"
+
+func init() {
+	database.AppendMigrate(&IotCommand{})
+	database.AppendMigrate(&IotOutbox{})
+	database.AppendMigrate(&IotDeviceMessage{})
+}