ENH: Add ability to load bands as data_vars

[snowman2]

@alexamici brought this up in #197 and has been something I have thought about for a while and haven't come up with a great solution yet.

xarray-gdal implementation: https://github.com/bopen/xarray-gdal/blob/main/xarray_gdal/xarray_plugin.py

Benefits:

• It could potentially enable round-trip loading in of data as in Roundtrip export and import of Dataset object to maintain same structure? #249
• Would provide a nice mechanism to store band specific attributes in each variable (possible fix for Store band specific attributes in coordinates #81)

Why hasn't it been done already?

• Backwards compatibility/consistency with xarray.open_rasterio
• Loading it as a DataArray allows open_rasterio to work with multidimensional files where the band is a coordinate (time).
• The coordinate mechanism provides a nice interface for selecting the band you are interested in by an index rds.sel(band=1).

It may make sense to have an option such as band_as_variable where you can toggle this mode on.

[ashleysommer]

This looks like a really useful feature (and directly related to my issue in #484)

In the gdalbuildvrt tool, you can pass the option -separate that puts each file into a separate band in the VRT file (and in this case each source file can have a different dtype).

So I propose, if you make this an optional behavior, the option could be called separate.

[snowman2]

Related:

• Band Tags missing #525
• How to see `tags` in GeoTiff? #573

[snowman2]

For those interested, see #600.