[bug#31432] [PATCH 0/2] gnu: Add lightgbm and vowpal-wabbit.

[Fis Trivial]

Language bindings are not enabled for vowpal-wabbit, it requires
rewritting the build code. Anyway, it has a fully featured command line
interface, so the language bindings can wait.

GPU support is not enabled for lightgbm, as GUIX doesn't have GPU
toolchain. I put this in the package features description.

I will send the two packages in one thread although they are not related
in the dependency tree. If you prefer me to send those with different
thread, just tell me. :)