defaults for storage_options for the s3 protocol

[keewis]

• follow-up to the discussion in Opening http remote files still not working with defaults #135

There are multiple different ways of how to authenticate S3: passing explicit kwargs to storage_options, but also environment variables and a session profile (where the credentials are read from a config file, like .aws/credentials).

The current defaults in

VirtualiZarr/virtualizarr/utils.py

Line 48 in fdab54c

protocol_defaults = {"key": "", "secret": "", "anon": True}

assume we always want to use kwargs for S3, but that will actively prevent other methods from working. For example:

from aiobotocore.session import AioSession

open_virtual_dataset(url, reader_options={"storage_options": {"session": AioSession(profile="myprofile")}})

will not use the passed profile because s3fs / aiobotocore prioritize the kwargs.

The only thing I can think of to fix this is to simply remove key and secret, but not sure if that's the best option.

[TomAugspurger]

IMO, virtualizarr shouldn't have default storage options. I don't think it's in a better position to pick defaults than the underlying library.

[norlandrhagen]

Totally agree. This PR takes a stab at removing those defaults.

[keewis]

should have been closed by #228