archive: add buffers to operations with tarballs

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
archive: add a benchmark for TarUntar

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
[DOCS] replace foo/bar with concrete names

namespaces are not well documented, and I had to jump around to other docs. replacing `foo/bar` hopefully makes what's going on here a bit more obvious.

Docker-DCO-1.1-Signed-off-by: Tim Ruffles <timruffles@gmail.com> (github: timruffles)
Merge pull request #7108 from unclejack/archive_speedup

speed up archive
Merge pull request #7181 from timruffles/patch-3

[DOCS] replace foo/bar with concrete names