Add support for zstd compression via external tooling

This patchset has been forward-ported from the initial delta introduced in Ubuntu by @athos as mentioned in !65 (closed).

As you might know, Ubuntu has moved to zstd as the default compression algorithm used in dpkg, while this particular algorithm isn't implemented in Debian's dpkg. Furthermore, the Python packages shutil and tarfile don't support this algorithm either, which is why the approach used here is to invoke the zstd CLI as a subprocess, piping it the data.