Add generated code and takeoff example

[dieguit]

This PR adds generated rust files for every plugin, and allows access to the full grpc api with type safety.

Instead of manually writing rust code for every service, request and response, it exposes the client generated by tonic_build. Making the library unopinionated and 100% dependant on the grpc server definitions. I consider this approach more mantainable, as there is already some effort in the mavlink organization to keep the mavlink_server and it's proto files running correctly for other SDK wrappers.

I also added an example for takeoff and land, where multiple plugins are tested at the same time.

There have been previous discussions about using FFI, I did a quick test and I was not able to get the bindings working correctly, so if somebody with C++ experience wants to help, I'd be happy to try again.

[julianoes]

Wow, that's amazing! Thanks for your work. Looking forward to giving it a try.

[FilipPyrek]

Great new PR! What about merging it? 😊

I'm trying to get to drones and Rust at the same time... and any improvements to this library are very helpful for me 🙂

[julianoes]

Right, I'm not really the maintainer here, so I was leaving it to @danieleades or @irsdkv to merge.

Also, CI seems to fail, so that's something to check before merging, I assume.