Add context builder

[routiful]

Hello :)

I've studied Rust since last year and I've been developing some applications with Rust. ROS client library in Rust is the best approach to write solid nodes and packages. As one of ROS users, I should contribute features so that many ROS users can use this.

To make context builder is assigned to @DS3a, https://github.com/ros2-rust/ros2_rust/issues/206. However, it hasn't developed since last year. Thus, I commited that to support various features such as domain_id.

@huchijwk