R1:3573170dfacb

Compress file downloads if the client sends "Accept-Encoding: gzip" and we guess the file might compress alright

Summary:
Ref T13507. We currently compress normal responses, but do not compress file data responses because most files we serve are images and already compressed.

However, there are some cases where large files may be highly compressible (e.g., huge XML files stored in LFS) and we can benefit from compressing responses.

Make a reasonable guess about whether compression is beneficial and…