add

trading_assistant_api/common/codes/codes.go

@@ -0,0 +1,12 @@
+package codes
+
+type Code string
+
+const (
+	OK               Code = "ok"
+	InvalidInput     Code = "invalid_input"
+	Unauthorized     Code = "unauthorized"
+	Conflict         Code = "conflict"
+	InternalError    Code = "internal_error"
+	MethodNotAllowed Code = "method_not_allowed"
+)