feat: add basic slice definitions files for Focal

[cjdcordeiro]

Duplicate of #41, with a different base branch.

This PR backports (from 22.04) and fits a few (the most basic and essential) slice definitions files into the new Focal Chisel release.

The affected packages are:

• base-files
• base-passwd
• ca-certificates
• libc6
• libgcc-s1

The choice of packages was driven by our Chiselled Ubuntu base image.

[rebornplusplus]

Looks good to me now. Thanks.

Although I would have wished the libc6_libs slice definition could be a bit shortened; some of the lines may be merged together. But that'd just increase the likelihood of missed errors. It's better to be explicit, for now at least.

[cjdcordeiro]

Looks good to me now. Thanks.

Although I would have wished the libc6_libs slice definition could be a bit shortened; some of the lines may be merged together. But that'd just increase the likelihood of missed errors. It's better to be explicit, for now at least.

Yeah I think we should change a bit our approach towards the usage of globs. I don't think we should be using them as a way to be "lazy" about writing the full paths or trying to merge multiple paths into one, but rather as a way to reduce path duplication due to metadata properties of the path (like the architecture or version). For example:

• /usr/lib/*/libfoo*: IMO this is bad
• /usr/lib/*-linux-*/libfoo-2.*.so: this is better