Bring back the examples directory

[BrandonSimoncic]

I've been writing packages in ros2_rust for a few months at this point. And I see the examples directory was removed to improve maintainability.

The examples directory is not only a great resource for the code examples but also the Directory Structure and file management. I understand it can be difficult to maintain but even an example cargo.toml with all the possible ways to include things like metadata, how to implement a launch file with rust, all really helpful and not super transparent yet.

A fork with just examples would be nice!

[esteve]

@BrandonSimoncic unfortunately the example packages were causing issues with Cargo workspaces (see colcon/colcon-cargo#65), so we decided to move the examples to a separate repository (https://github.com/ros2-rust/examples). We've updated the instructions (e.g. https://github.com/ros2-rust/ros2_rust/blob/main/ros2_rust_kilted.repos#L30) to also clone the examples repo when using vcs import, so it should be functionally equivalent to having an examples directory in the ros2_rust repo.