Add `make_data_or_index_source` to the `storage` interface, implement it
for `filesystem_storage` storage which just creates `data_source` from a
file and for the `s3_storage` create a (maybe) decrypting source from s3
make_download_source.
This change should solve performance improvement for reading large objects
from S3 and should not affect anything for the `filesystem_storage`.
(cherry picked from commit 0de61f56a2)
4ffd72e597