[📑 Docs]: Normalize structure: Creating ephemeral application previews with LocalStack and GitHub Actions

What docs changes are you proposing?

Source: https://docs.localstack.cloud/aws/tutorials/ephemeral-application-previews/

What’s missing

• Intro
• Prerequisites
• Architecture diagram
• Steps
• Testing the application
• Conclusion

Proposed edits

• Add ## Architecture diagram of the preview flow.
• Add ## Testing the application checklist (preview URL reachable, smoke tests pass).

Acceptance criteria

• Diagram + Testing the application sections exist.

Code of Conduct

• I agree to follow this project's Code of Conduct