Retrieves the current CAs for a group.Show details from next link. https://docs.aws.amazon.com/ja_jp/cli/latest/reference/greengrass/list-group-certificate-authorities.html
| aws greengrass list-group-certificate-authorities \ |
| ListGroupCertificateAuthorities - AWS Greengrass : http://docs.aws.amazon.com/greengrass/latest/apireference/-greengrass-groups-groupid-certificateauthorities.html |