Support finding token for subdomain of a terraform registry

[wazy]

A terraform registry that redirects to a subdomain for the module url will cause terragrunt to find the token on the initial request but error out on the second request to the subdomain.

For example setting a source such as tfr://spacelift.io/<company>/<module_name>/aws?version=0.0.1 will fail.

The first request succeeds requesting <spacelift.io>:
https://spacelift.io/.well-known/terraform.json

But the second request to download the module fails since the hostname is now <app.spacelift.io> which isn't in the credentials.tfrc.json:
https://app.spacelift.io/registry/modules/v1/<company>/<module_name>/aws/0.0.1/download

[yhakbar]

Thanks for creating this, @wazy . Looking forward to the tests being added in #4445 so that we can verify your contribution works correctly.