[Agentic AI on EKS] Support arm64 container images and run on graviton instances

Update the eks reference implementation to support arm64

- Update eks auto mode to deployment to create a nodepool that provides arm64 ec2 instances, the default `general-purposes` only support amd64
- Update the helm charts for the pods to request arm64 using [node selector](https://karpenter.sh/docs/concepts/scheduling/#selecting-nodes)
- Update the build scripts and instructions to build containers images supporting linux/arm64
- Update the [test scripts](https://github.com/aws-samples/sample-agentic-frameworks-on-aws/blob/main/eks/scripts/containers.sh#L17-L27)
- Update the markdown files were we tell the user to run `docker build` or `finch`