docs: Update v20 upgrade guide to clarify that `"CONFIG_MAP"` is not a supported access type#3279

bryantbiggs merged 1 commit intoterraform-aws-modules:masterterraform-aws-modules/terraform-aws-eks:masterfrom

bryantbiggs:docs/configmapbryantbiggs/terraform-aws-eks:docs/configmapCopy head branch name to clipboard