add global exception handler for controllers

add new not found exception, add new test for ShopController

src/main/kotlin/com/example/demo/responses/ResponseStatus.kt

@@ -0,0 +1,7 @@
+package com.example.demo.responses
+
+import com.fasterxml.jackson.annotation.JsonValue
+
+enum class ResponseStatus(@JsonValue val status: String) {
+    NOT_FOUND("not found");
+}