add ContainerInsights rack parameter

[ntner]

Summary

• Adds ContainerInsights rack parameter (Yes/No, default No) to enable CloudWatch Container Insights on the ECS cluster
• Applies to Fargate workloads; EC2 Container Insights requires the CloudWatch agent daemon (follow-up)
• Default No preserves existing behavior and avoids unexpected cost (~$15-25/month per rack when enabled)

Parameter	Type	Default	Effect
ContainerInsights	Yes/No	No	Enables CloudWatch Container Insights on the ECS cluster

CloudFormation Impact

• Cluster resource (logical ID: Cluster): UPDATE only (adds ClusterSettings property). No REPLACE.
• New condition: ContainerInsightsEnabled
• No Outputs changed, no resource IDs changed, no imports affected

Downgradability

Safe. Removing the parameter on downgrade reverts ClusterSettings to the AWS default (disabled). No CF parameter gets stuck because default No preserves existing behavior.