feat: add initial test setup with Vitest for demo purposes

Author: nicosammito

actions/shopware-action/test/index.test.ts

@@ -0,0 +1,8 @@
+import "reflect-metadata";
+import {describe, expect, it} from "vitest";
+
+describe("Demo test", () => {
+    it("Demo test", () => {
+        expect(true).toEqual(true)
+    });
+});