We need to support new style APT repo signatures

Author: @quba42 (quba42)

Redmine Issue: 8953, https://pulp.plan.io/issues/8953

See the following specification: https://wiki.debian.org/Teams/Apt/Spec/AptSign

See the following excerpt from IRC:

Conan Kudo
quba42: judging by what's going on, I expect this to launch in Debian 11
it definitely will be part of Ubuntu 22.04
I'm also having a conversation with the RPM folks about whether we might want to consider this for the RPM ecosystem in the future too
because not having an independent implementation from OpenBSD's signify was the main problem for me
now that two exist now (one in C++ and another in Python), I think this is something worth pursuing in the RPM ecosystem
Conan Kudo
quba42: my understanding is that Debian 11 and Ubuntu 22.04 will have both, but immediately afterward GPG will be dropped
quba42: apt-key(8) has already been marked for removal after Debian 11 release
(which is where the gpg key management is in apt)
https://www.mankier.com/8/apt-key
I guess this means I'm packaging up the new python-aptsign package for Fedora...
which means packaging python-apt too

Thanks Conan Kudo, for alerting me to this!

Start with the AptSign specification and the linked Redmine issue 8953, then review the referenced apt-key and python-aptsign context. The issue is complete when pulp_deb supports the new-style APT repository signatures, but it does not identify files or tests to guide the implementation.