[FEATURE] Add ECS deployment

Currently, the guide demonstrates how LiteLLM can be deployed into EKS. Extend the deployment section to show how LiteLLM can be deployed into ECS as well.

Use CDK as IaC.

Locate the deployment section that currently documents LiteLLM on EKS and review how its infrastructure examples are organized. Then identify the existing CDK entry points and determine how an ECS deployment should be documented alongside EKS. Done means the guide includes a usable ECS deployment path using CDK and remains consistent with the existing deployment instructions.

Written by the indexing model from the issue text.