Add a GET /config Route

[jameskbride]

Context

This PR adds a convenience endpoint at GET /config to retrieve the runtime configuration during development and testing.

Changes

• Expose GET /config.
• Add logging at start-up to indicate the /health and /config endpoint locations.

Testing and Validation Steps

1. Start the application via ./gradlew run.
2. Open http://localhost:9911/config in a browser (or make a GET /config request via cURL, POSTman, Insomnia, whatever).
3. ✅ Validate that the current JSON config is returned.
4. Make a change to the config: aws sns create-topic --endpoint-url http://localhost:9911 --name another-topic
5. Refresh the browser.
6. ✅ Validate that the config is updated.