Copying files with --symlink-install

The flag `--symlink-install` is currently not supported.
I think it is an important part as the argument is heavily used is ROS2.

It could be implemented by forwarding the flag to [cargo-ament-build](https://github.com/ros2-rust/cargo-ament-build) and writing a symbolic link alternative to the [copy function](https://github.com/ros2-rust/cargo-ament-build/blob/main/src/lib.rs#L135).