Opening a datatree from S3 bucket with zarr store

What happened?

Trying to open a datatree using the Zarr backend from a zarr file stored in a private S3 bucket leads to the following error:

GroupNotFoundError: group not found at path ''

This issue was already in the xarray-contrib/datatree, see https://github.com/xarray-contrib/datatree/issues/322
The fix could be more or less the same, but at that time I did not take time to propose a PR.

What did you expect to happen?

The open_datatree function from zarr.py has a storage_options argument. Yet this argument is not passed to the ZarrStore.open_store.

Minimal Complete Verifiable Example

import xarray.backends.api as xr_api
storage_options = { 
"s3": {
        "key": [access-key]
        "secret": [secret-key],
        "endpoint_url": [endpoint-url]
    }
}
dt=xr_api.open_datatree("s3://path/to/product",engine="zarr",storage_options=storage_options)
dt

MVCE confirmation

• Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• Complete example — the example is self-contained, including all data and the text of any traceback.
• Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• New issue — a search of GitHub Issues suggests this is not a duplicate.
• Recent environment — the issue occurs with the latest version of xarray and its dependencies.

Relevant log output

No response

Anything else we need to know?

A possible fix could be, in xarray.backends.zarr.open_datatree:

filename_or_obj = _normalize_path(filename_or_obj)
        if group:
            parent = NodePath("/") / NodePath(group)
            stores = ZarrStore.open_store(filename_or_obj, group=parent,storage_options=storage_options)
            if not stores:
                ds = open_dataset(
                    filename_or_obj, group=parent, engine="zarr", **kwargs
                )
                return DataTree.from_dict({str(parent): ds})
        else:
            parent = NodePath("/")
            stores = ZarrStore.open_store(filename_or_obj, group=parent,storage_options=storage_options)
        if storage_options:
            kwargs["backend_kwargs"] = {"storage_options": storage_options}
        ds = open_dataset(filename_or_obj, group=parent, engine="zarr", **kwargs)

As a summary:

• add storage_options in ZarrStore.open_store
• set backend_kwargs in open_dataset

Environment

Start in xarray.backends.zarr.open_datatree and inspect how ZarrStore.open_store and open_dataset receive storage_options. Ensure the private S3 path can be opened with those options, then verify that the datatree loads successfully using the provided example; the issue does not name a specific test file.