chore(medusa-test-utils): create declaration file (#6858)

**What**
- Fixes tsconfig to ensure a declaration file is included in the build.

**Why**
- Ensure tsserver can understand things from medusa-test-utils
- Get rid of "Could not find a declaration file for module" warning in editors.

packages/medusa-test-utils/tsconfig.json

@@ -4,7 +4,7 @@
     "target": "es5",
     "outDir": "./dist",
     "esModuleInterop": true,
-    "declaration": false,
+    "declaration": true,
     "module": "commonjs",
     "moduleResolution": "node",
     "emitDecoratorMetadata": true,