Use smaller image for FastAPI service

Define CloudFormation stack for deploying webapp to AWS using ECS.
Description:
- 1 Cluster, 2 availability zones
- 5 services: postgres + redis -> LangGraph API -> FastAPI backend -> NextJS frontend
- Tasks run by EC2 instances (t2.micro) in private subnet
- Auto scaling
- Load balancer for frontend
- NAT gateway for LangGraph API (outbound traffic to OpenAI API)
- Docker image saved in public ECR repository
- Secret API keys saved in AWS Secret Manager
- Postgres service has mounted EFS volume
- Implemented healthcheck
- Logging with CloudWatch

Create CD jobs
- Build & upload necessary Docker images to ECR
- Deploy to AWS ECS