add support for zstd compression

[hesmar]

Description of the Change

This PR adds support for zstd compressed data tar archives.

Checklist

• unit-test added (if change is algorithm)
• functional test added/updated (if change is functional)
• man page updated (if applicable)
• bash completion updated (if applicable)
• documentation updated
• author name in AUTHORS

[SteamedFish]

Debian is still using xz compression by default, doesn't currently support zstd.

Ubuntu has added zstd support since dpkg 1.19.2ubuntu1, and switched to zstd by default since dpkg 1.20.9ubuntu2.

For detailed information, please refer to this blog by Ubuntu maintainer: Hello zstd compressed .debs in Ubuntu!

[svanzoest]

@hesmar could this be extended to also support Zstandard compressed control files as described in deb(5)?

[rtreffer]

👋 I've been rebuilding some ubuntu 21.10 packages and added them with a patched aptly
0001-Add-zstd-support.patch.txt

The suggested change is also a bit invasive for the addition of zstd....

[r4co0n]

@rtreffer, could you please elaborate on what you consider invasive?

On a quick glance, it seems the new code branch should be part of if strings.HasPrefix(header.Name, "data.tar") {.

[rtreffer]

It pulls in a set of unrelated(?) go.mod and go.sum updates.

[rtreffer]

Invasive is a bit too strong, but there is a cleanup missing as far as I can tell :-)

[r4co0n]

@rtreffer, I am not a go developer and don't play one at work, but I am quite certain unrelated package updates should go via a separate pull request, blocking this one if they are strictly required.

[lbolla]

@hesmar do you mind cleaning up the go.sum/go.mod files (which seems to include unneeded packages) and rebase against master?

[lbolla]

@hesmar Would you mind rebasing against master: we have GH Actions to run tests on CI.

Also, unittests are missing for this PR. They are needed for it to be considered for merging. Thanks!

[lbolla]

Actually, I'm deprecating this PR in favor of #1002