Identify end-to-end testing opportunities for pull-request checks

[NimJay]

• Ideally, each sample in this repository would be throughly tested (end-to-end) — when a change is made to the sample (via a pull-request).
• This would allow us (reviewers) to more confidently merge changes into main.
• Example:
  • Deploy and ping the Node.js app at: /databases/hello-app-cloud-spanner/Dockerfile