Create docker-compose-aws.yml for local testing

### Overview

Create a docker-compose file that allows developers to test the AWS/production Docker setup locally before deploying. This helps catch configuration issues early.

### Action Items
- Create `docker-compose-aws.yml` that:
- Builds using `Dockerfile-aws`
- Uses `requirements-aws.txt`
- Runs the `entrypoint-aws.sh` script
- Starts gunicorn (not runserver)
- Includes database service for local testing
- Add documentation explaining how to use the file for testing
- Test that the setup works locally without issues

### Acceptance Criteria
- `docker-compose-aws.yml` exists and builds successfully
- App starts with gunicorn and serves static files
- Database migrations run correctly
- Developers can test the production setup locally
- Instructions are documented for developers

**Parent Issue**: #219
**Blocked by**: #219 sub-issue "Add gunicorn and Whitenoise, and set up Dockerfile-aws and entrypoint-aws.sh"