Package name mapping across backends

[trmxvibs]

Package names differ across distros for the same software (e.g.
python3-pip on apt vs python-pip on pacman vs py3-pip on apk).
Currently pkgwrap passes the name through unchanged, so users must know
the right name for their OS. A mapping table (even a small curated one
for common packages) would remove a major pain point.

[kaminimangal]

@trmxvibs Can you assign this to me? I'd like to work on it — plan is a small mapping table for common packages across apt/pacman/apk/dnf, with fallback to the original name if unmapped.