Figure out appropriate STAC metadata for block shapes and dtype

[TomAugspurger]

Right now stac_vrt requires two external pieces of information: the data type and block shapes:

>>> vrt = stac_vrt.build_vrt(stac_items, data_type="Byte", block_width=512, block_height=512)

which eventually make up the GDAL data_type and BlockXWidth and BlockYWidth in the VRT. Presumably these can come from a STAC extension.

[TomAugspurger]

https://github.com/stac-extensions/file looks to provide data_type, specifically https://github.com/stac-extensions/file#data-types.

[matthewhanson]

If data_type is provided that's great, but if not, I think the asset should be queried for it's data type. It would be a shame if the file extension is required.

For the block size, it's optional, and there is no extension for which this is included. But I'm also not clear on how this is used. For the underlying assets the block size makes sense as it represents how the data is actually stored. But in a VRT it's just referencing other files so what would setting it to a different block size do? What if you have multiple files with different block sizes?