Use xz instead of gzip version of Package files

[mikberg]

We encountered a problem where we weren't able to use buster-backports, and traced this down to update_deb_packages only considering Package.gz files. For buster-backports, these files are only available as Package.xz.

See: https://wiki.debian.org/DebianRepository/Format

It seems to me like it would be better to switch to download Package files in the xz format. Alternatively, a fallback-mechanism could be implemented.

[mikberg]

This PR can be tested with

http_archive(
    name = "rules_deb_packages",
    sha256 = "04fdc320a5f5efc2d5ce6690bbd7bc5f5855a211ec803d53411dd1529aa17cf3",
    urls = ["https://github.com/mikberg/rules_deb_packages/releases/download/v0.4.1-test/rules_deb_packages.tar.gz"],
)

and

sources = [
            "http://deb.debian.org/debian buster main",
            "http://deb.debian.org/debian buster-backports main",
]

[PeterMylemans]

Hi @mikberg

Thank you for your contribution and sorry for the delay in reviewing!

Looks like a good solution, but I would prefer a fallback implementation. Not all repositories seem to publish .xz archives (even though the spec prefers it). I guess they are using an older version of the repo publishing software.

E.g. http://repos.azul.com/zulu/deb/dists/stable/Release (Zulu OpenJDK) publishes gz en bz2 instead of xz.