update handling of zstd in tutorials

[rsignell-usgs]

no need to uncompress the zstd JSON to disk -- fsspec can handle it!

For example:

%%time
fs = fsspec.filesystem("reference", fo='s3://esip-qhub-public/ecmwf/era5_multivar_197901_202205.json.zst', 
                       ref_storage_args={"compression": "zstd" ,'skip_instance_cache':True},
                       remote_protocol='s3', remote_options={'anon':True})
m = fs.get_mapper("")
ds = xr.open_dataset(m, engine="zarr", backend_kwargs={'consolidated':False}, chunks={'time0':288})
ds

also perhaps create an intake catalog for the smaller and larger ERA5 virtual datasets?