Upcoming AWS change in ARN format breaks `emp ps`

[tyrken]

AWS have long had an option to use a new format for ECS arns for services, tasks and container-instances, see https://aws.amazon.com/blogs/compute/migrating-your-amazon-ecs-deployment-to-the-new-arn-and-resource-id-format-2/
What's new is that from October 2020 these options default to on for new accounts, and April 2021 they become mandatory for all accounts. So from that latter date our existing empire controllers will see a mix of old & newer formats.

I've tested this by making a new account with the options turned on and it mostly works. The only fault I've found so far is that emp ps breaks, giving a "invalid ARN resource" error, likely from

empire/pkg/arn/arn.go

Lines 63 to 77 in 7ab6b86

	// SplitResource splits the Resource section of an ARN into its type and id
	// components.
	func SplitResource(r string) (resource, id string, err error) {
	p := strings.Split(r, "/")
	if len(p) != 2 {
	err = ErrInvalidResource
	return
	}
	resource = p[0]
	id = p[1]
	return
	}

Anybody else come across this?