Separate web_video_server into a component and an executable

[jwdinius]

Public API Changes

• To support composition, web_video_server::WebVideoServer now inherits from rclcpp::Node. Previously, the WebVideoServer class had a private member variable node_ for interacting with the ROS 2 runtime.
• The constructor for WebVideoServer was changed to accept a single input argument of type rclcpp::NodeOptions. This is required for components.
• The spin method was removed. This separates the definition of work from the means of executing it. Instead of the WebVideoServer needing to have a public method for spinning the private node_ member, the executor that does the work is now created outside of the class.

Description

The ROS 2 (Humble) docs recommend writing applications as components:

By making the process layout a deploy-time decision the user can
choose between:

• running multiple nodes in separate processes with the benefits
  of process/fault isolation as well as easier debugging of individual
  nodes and

• running multiple nodes in a single process with the lower overhead
  and optionally more efficient communication.

The default deployment scheme for the web_video_server node remains the same: i.e., using
ros2 run web_video_server web_video_server {parameter-args-here}.

Having a component library available adds flexibility for users, particularly for those users looking to use intra-process memory for published camera topics and the web video server.

[bjsowa]

Thanks for the contribution! I remember trying to do a similar thing but I found it problematic for WebVideoServer to inherit from rclcpp::Node. Don't remember the exact issue though and this seems to work.

[jwdinius]

@bjsowa I have addressed your comments. Thanks for the suggestions!