make modo add remote-compatible

[cmdoret]

Modo add creates a folder locally. To support remote write operations we can directly "mount" the s3 folder

Requirements:

• rely on zarr's built-in s3 support to update metadata transparently
• use s3fs (?) to manually upload / remove / delete files on s3

note for now we ignore access control and use anon buckets

[almutlue]

Re metadata update:

• add works without adaptation using the current implementation, if an s3_endpoint is set.
• zarr.consolidate_metadata(zarr.Group) does not work properly for remote endpoints (looks related to: FSStore not handling .zmetadata correctly when dimension_separator is set to / at store level. zarr-developers/zarr-python#1121)
• remove does not work, even if the s3_endpoint is set (why)

TODO

• find a fix for consolidate_metadata with remote objects
• fix remove for remote storage
• adapt cli to work with remote objects