Example for `aws eks update-kubeconfig` needs markdown formatting

[tim-finnigan]

Describe the issue

Values like --role-arn should be in markdown.

Links

• https://awscli.amazonaws.com/v2/documentation/api/latest/reference/eks/update-kubeconfig.html
• https://github.com/aws/aws-cli/blob/develop/awscli/examples/eks/update-kubeconfig/_description.rst?plain=1