Bundle iceoryx C++ sources for offline builds

[elBoberido]

Bundle iceoryx C++ sources instead of fetching them via git. This will fix the documentation on docs.rs.

From https://kornel.ski/rust-sys-crate#donts

Avoid downloading anything. There are packaging and deployment tools that require builds
to run off-line in isolated containers. If you want to build the library from source,
bundle the source in the Cargo crate.

Cargo build process is supposed to be entirely self-contained and work off-line.