Support lazy `save_dataset` ?

[rajwanir]

Hi

I realize that the save_dataset function doesn't return the delayed object. For instance, if ran with compute=False:

https://github.com/sgkit-dev/sgkit/blob/eef911e87d1aad47cb139170bcda1b82f220114f/sgkit/io/dataset.py#L71

running save_dataset with compute=False has use cases for example - visualizing the graph or just initializing the directory without writing chunks etc. I could to use the xarray.dataset.to_zarr but the fix for filters is good in save_dataset so thought to bring it up for everyone use.

Thank you.