add `use_zarr_fill_value_as_mask` in `open_datatree` for Zarr Stores

[vincentsarago]

Maybe I'm totally mistaken but it seems that use_zarr_fill_value_as_mask option is not available when using xarray.open_datatree for a Zarr store, while it's available for open_dataset

xarray/xarray/backends/zarr.py

Lines 1770 to 1808 in d022da5

	def open_datatree(
	self,
	filename_or_obj: T_PathFileOrDataStore,
	*,
	mask_and_scale=True,
	decode_times=True,
	concat_characters=True,
	decode_coords=True,
	drop_variables: str | Iterable[str] | None = None,
	use_cftime=None,
	decode_timedelta=None,
	group: str | None = None,
	mode="r",
	synchronizer=None,
	consolidated=None,
	chunk_store=None,
	storage_options=None,
	zarr_version=None,
	zarr_format=None,
	) -> DataTree:
	filename_or_obj = _normalize_path(filename_or_obj)
	groups_dict = self.open_groups_as_dict(
	filename_or_obj=filename_or_obj,
	mask_and_scale=mask_and_scale,
	decode_times=decode_times,
	concat_characters=concat_characters,
	decode_coords=decode_coords,
	drop_variables=drop_variables,
	use_cftime=use_cftime,
	decode_timedelta=decode_timedelta,
	group=group,
	mode=mode,
	synchronizer=synchronizer,
	consolidated=consolidated,
	chunk_store=chunk_store,
	storage_options=storage_options,
	zarr_version=zarr_version,
	zarr_format=zarr_format,
	)

Looking at

xarray/xarray/backends/zarr.py

Lines 1840 to 1851 in d022da5

	stores = ZarrStore.open_store(
	filename_or_obj,
	group=parent,
	mode=mode,
	synchronizer=synchronizer,
	consolidated=consolidated,
	consolidate_on_close=False,
	chunk_store=chunk_store,
	storage_options=storage_options,
	zarr_version=zarr_version,
	zarr_format=zarr_format,
	)

it seems that we should be able to forward a use_zarr_fill_value_as_mask option

cc @d-v-b