Describe the enhancement

Currently terragrunt fails if a source other than git or local is defined in stacks

stack "mystack" {
    source = "gcs::https://www.gogleapis.com/storage/v1/my-bucket/stack"
}

Additional context

The effor is super small, a simple change in in the copyFiles method in pkg/config/stack.go is enough.

PoC (Proof of Concept)

s3 and gcs should be usable in source

stack "mystack" {
    source = "gcs::https://www.gogleapis.com/storage/v1/my-bucket/stack"
}

RFC Not Needed

• I have evaluated the complexity of this enhancement, and I believe it does not require an RFC.