Combine the LogStreamByteStream and CAS ByteStream services
Description
Currently these services can't be deployed in the same instance, which means its possible to deploy an all-in-one BuildGrid for every component except LogStream.
This MR addresses this issue by combining the two conflicting ByteStream servicers into one general ByteStream servicer which is capable of handling requests for LogStream and CAS resources if configured to do so, handing them off to the correct backend.
It also includes the necessary extensions to the configuration to allow the ByteStream for LogStream to be configured separately.