Refactor Rust crate avoid build

[jlloh]

Originally had this MR to fix the build for Mac M1. #2160 .

After testing this in my environment, I realised that with the current implementation:

1. The current implementation does not allow the crate to be easily published to crates.io due to dependencies on the base repo as it compiles the shared library from source
   • This repo is actually pretty big, and if caching this for CI, it is >1GB and affects build speed pretty significantly
2. Looking at how onnxruntime's rust bindings and pytorch's rust bindings download the shared library (in this case libcatboost.so/dylib) over building it
3. Taking inspiration from that, I modified catboost-sys to download the libcatboost shared library from github releases (and did a soft link to ../../libs/model_interface to allow bindgen to generate the necessary rust bindings. I managed to publish the crate here.
4. After that, I subsequently changed the dependencies for the actual crate itself and published it to here.
   • Note that I had to call the crate catboost-rs instead of catboost because there's an existing empty crate already using that name, preventing me from using it

Note that for now in build.rs I check for apple + aarch64 before downloading the dylib, as that's the machine I have. I don't have a non-M1 mac to test if that works fine.

Would like to get feedback on whether this is a reasonable approach, and can be merged into master.

I hereby agree to the terms of the CLA available at: https://yandex.ru/legal/cla/?lang=en.

[jlloh]

Minor update: As I haven't heard back from the maintainers, and it seems like overkill to fork the whole repo and maintain it, I have opted to split out the code to it's own repository, similar to onnxruntime-rs, since all I need are the files in catboost/libs/model_interface for catboost-sys.

Instead, to build catboost-sys, the user is responsible for cloning the catboost repo himself and set an environment variable CATBOOST_DIR.

The crate is published here.

Leaving the MR open for now in case the maintainers ever see it.