Add support for Amazon ECS on Fargate

## Description
Request to add support for Amazon ECS Services running on Fargate to the CloudWatch Dashboard Generator tool.
ECS is a commonly used container orchestration service that would benefit from monitoring during Countdown scenarios.

## Proposed Implementation
Add ECS support with the following dimensions:

- **Namespace**: `AWS/ECS`
- **Dimensions**:
- `ClusterName` and `ServiceName` for ECS Services
- **Metrics**:
- CPUUtilization
- MemoryUtilization

If ContainerInsights enabled:
- **Namespace**: `ECS/ContainerInsights`
- **Dimensions**:
- `ClusterName` and `ServiceName` for ECS Services
- **Metrics**:
- TaskEphemeralStorageUtilization
- DesiredTaskCount
- RunningTaskCount

## Expected CSV Format
service,region_code,dim1_name,dim1_value,dim2_name,dim2_value
ECS,us-east-1,ClusterName,my-cluster,ServiceName,my-service

Start by reviewing how the Python CLI represents its existing AWS service support and how it consumes the documented CSV dimensions. Add ECS Fargate entries for the AWS/ECS and ECS/ContainerInsights namespaces, including the listed dimensions and metrics, then verify that the expected CSV format produces the requested dashboard configuration.

Written by the indexing model from the issue text.