Move Buildroot feature example

[uilianries]

It's an example from Conan Community, now archive.

https://github.com/conan-community/buildroot

I'm going to update the documentation too.

This PR is large because Buildroot distributes one file for each package + scripts needed for building. As it generates an embedded Linux image and need to build bootloader, kernel and rootfs, it takes 2h to build everything. Thus, I excluded it from CI job.

The only thing which should be considered to be reviewed is README.md

If you want to know how does it work, read https://docs.conan.io/en/latest/integrations/cross_platform/buildroot.html

Requires #76 first

[memsharded]

I would say that embedding those many files we don't really produce here, should be avoided. Isn't it possible to get those files with a git clone, a download + unzip from elsewhere? It would be enough to document it

[uilianries]

Good idea, yes, we can download and apply our changes.

[uilianries]

@memsharded I reduced buildroot example, it's much much less than before.

conan_config file is a recipe which tells to Buildroot what should be built or not. It's not mandatory, it's a configuration file. Without it the user would need run make menuconfig and mark all Conan flags. Not hard, just operational.

The diff comes from Conan Community, but updated with latest Conan version (1.33) and packages. As it's not a git folder, I used diff -ruN to extract the patch file.

Still, we can't run it on CI, because buildroot build ALL from sources, bootloader, kernel, packages, ... just like Yocto, it takes hours.