A BlobReader can be used to read a blob, which might consist out of
multiple chunks. Chunks are fetched from a ChunkService.
Change-Id: I1806225b0052adaa4a2320b79b744e554e524ee3
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8088
Tested-by: BuildkiteCI
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Reviewed-by: tazjin <tazjin@tvl.su>
