add eksctl to the base image

[miparnisari]

See https://docs.aws.amazon.com/eks/latest/userguide/getting-started-eksctl.html

i need this so I can run

eksctl create iamidentitymapping \
              --cluster ${{ secrets.CLUSTER }} \
              --region ${{ secrets.AWS_REGION }} \
              --arn ${{ secrets.AWS_IAM_ROLE }} \
              --group system:masters \
              --no-duplicate-arns \
              --username github-action