chore(eks): add back package.json in test app

A package.json in a test app was accidentally removed as part of the
repo restructure. This is used as part of the yarn upgrade workflow and
if it is absent then the ncu command will apply to the `aws-cdk-lib` package.
https://github.com/aws/aws-cdk/blob/1f4c4fafe22bdd80c43e80e8a968428f3aa827e1/.github/workflows/yarn-upgrade.yml#L70

Author: corymhall

packages/aws-cdk-lib/aws-eks/test/sdk-call-integ-test-docker-app/app/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "eks-service-account-sdk-call-integ-test",
+  "private": "true",
+  "dependencies": {
+    "aws-sdk": "^2.1373.0"
+  }
+}