Derive product type if not explicitly given

[konstntokas]

We should try to get rid of product_type_name, and extract the product type from the file name; it is possible for a FSMap from fsspec via root; it is possible for zarr.DirectoryStore; I think this should cover most cases.

[forman]

We should try to get rid of product_type_name

There may still be situations where the product type name cannot be derived. I also dislike that we would then rely on the naming pattern of a filename - no good practice. So let's keep it, which is also less work.

it is possible for a FSMap from fsspec via root; it is possible for zarr.DirectoryStore

That's fine and should be used if product_type is not given.

[konstntokas]

• Document that this parameter is only used in rare cases -> adjust docstring in open_datatree and open_dataset
• get the path from the store instance, if possible