Use ETag in streaming mode to detect resource updates

**Is your feature request related to a problem? Please describe.**

I want to cache data I generate from processing a dataset I've loaded in streaming mode, but I've currently no way to know if the remote data has been updated or not, thus I don't know when to invalidate my cache.

**Describe the solution you'd like**

Take the ETag of the data files into account and provide it (directly or through a hash) to give a signal that I can invalidate my cache.

**Describe alternatives you've considered**

None