Does external references support remote storages (fsspec)?

[ketozhang]

Does asdf support external references to remote storages? I know fsspec is supported, so if it uses the same open implementation, then this should work.

It would look something like this:

import asdf
from asdf import AsdfFile
af = AsdfFile()
external = asdf.open('s3://path/to/data.asdf')
af.tree['my_ref_a'] = external.make_reference(['a'])

#ASDF 1.0.0
#ASDF_STANDARD 1.6.0
%YAML 1.1
%TAG ! tag:stsci.edu:asdf/
--- !core/asdf-1.1.0
asdf_library: !core/software-1.0.0 {author: The ASDF Developers, homepage: 'http://github.com/asdf-format/asdf',
  name: asdf, version: 5.3.0}
history:
  extensions:
  - !core/extension_metadata-1.0.0
    extension_class: asdf.extension._manifest.ManifestExtension
    extension_uri: asdf://asdf-format.org/core/extensions/core-1.6.0
    manifest_software: !core/software-1.0.0 {name: asdf_standard, version: 1.5.0}
    software: !core/software-1.0.0 {name: asdf, version: 5.3.0}
my_ref_a: {$ref: s3://path/to/data.asdf#a}
...