Currently, it isn't possible to use Nautilus for the extraction of the
".zstd" and ".tar.zst" archives. However, it seems that this compression
is supported by the libarchive library nowadays. Let's add the
`application/zstd` and `application/x-zstd-compressed-tar` mime-types
to the list of supported. This will allow Nautilus to show the "Extract"
and "Extract to..."  actions.

Related: nautilus#2860