PEPhubclient should correctly handle domains for registry paths

If I make a looper config file with a weird, bogus registry path like this:

pep_config: bogus-website.com://databio/pep_derived_attrs:default
output_dir: results
pipeline_interfaces:
  - pipeline/pipeline_interface.yaml

It is actually ignoring the domain information, and just grabbing the databio/pep_derived_attrs:default section, and retrieving it from pephub, and running the pipeline correctly.

This means we're not handling the domain right. We're only allowing pephub.databio.org, regardless of what you put in the domain. This means we can't allow people to use this with a registry other than ours.

Instead, we can default to the main interface, but we need to allow the user to specify an alternative domain. What if I want to try this on a local instance, using localhost://registry_path? This is not currently possible.

Not sure if this is something to be fixed in looper or in PEPhubClient.