Replace dpkg.list et al

[zeha]

Currently there are two automated consumers of dpkg data:

1. our own grml-live build-drivers uses dpkg.list output
2. jenkins.debian.net uses dpkg selections, via https://salsa.debian.org/qa/jenkins.debian.net/-/blob/master/bin/reproducible_create_meta_pkg_sets.sh

Given we don't really like the dpkg.list format, and want to get rid of the other files, maybe we can produce a tails-style build-manifest file. If it ends up being compatible with what jenkins.debian.net parses here, that would save implementation time for them too: https://salsa.debian.org/qa/jenkins.debian.net/-/blob/master/bin/reproducible_create_meta_pkg_sets.sh?ref_type=heads#L32

[mika]

I wasn't aware of this tails-style build-manifest file (TIL!), I very much like this and would love to see us follow this approach with Grml!