Add Terraform setup for Elastic Beanstalk Docker deployment

[Subhransu-De]

What to build

Add a Terraform infrastructure setup under /infra that deploys this FastAPI template to AWS Elastic Beanstalk using Docker. This setup should provide a legacy/PaaS-style AWS deployment path for users who want Elastic Beanstalk to manage the EC2, load balancer, autoscaling, and deployment lifecycle around the Dockerized app.

Acceptance criteria

• Terraform provisions an Elastic Beanstalk application and Docker-based environment.
• The setup supports configuring instance type, environment name, app version/source bundle, health check path, and scaling basics.
• The FastAPI app is reachable through the Elastic Beanstalk environment URL.
• Environment variables and secret references are supported or clearly documented.
• Logs and health reporting are configured or documented.
• Outputs include Elastic Beanstalk application name, environment name, CNAME, and URL.
• Documentation explains how to package/deploy the Docker app version and how this setup differs from ECS.
• A verification command is documented for checking the deployed health endpoint.

Blocked by

None - can start immediately.