Read from public S3 URI without credentials

[pgarrison]

Problem

No credentials are required to read from a public S3 bucket. However, ome-zarr-py requires credentials when using an s3:// url. https:// urls do not face this issue.

Example (run without any AWS credentials configured):

from ome_zarr.io import parse_url
from ome_zarr.reader import Reader

url = (
    "s3://allencell/aics/nuc_morph_data"
    "/data_for_analysis/baseline_colonies/20200323_09_small/raw.ome.zarr"
)
reader = Reader(parse_url(url))  # Logs "botocore.exceptions.NoCredentialsError: Unable to locate credentials" and raises AttributeError 

Possible fixes

The core of the issue is that s3fs requires the anon=True parameter to use a public bucket without credentials.

• Support init of ome_zarr_py.io.ZarrLocation with zarr.storage.FSStore #349 would resolve this, since the user can create their own FSSpec instance with anon=True
• Another option would be to accept a kwargs argument to Reader.__init__ that gets passed along to FSSpec