feat: New parameter and cli arguments handling

[bjsowa]

Let's be honest here. The way parameters are passed down from rosbridge_server to the Rosbridge protocol and internal classes is a complete mess:

• Rosbridge library retrieves some parameters either from:
  1. Protocol.parameters dictionary.
  2. Node handle parameters.
  3. Class variables overwritten by rosbridge_server.
• RosbridgeWebsocketNode parameter handling is very complex. It's very hard to tell which parameters relate to the server and which are passed to the protocol.
• The cli argument parsing contains a lot of repeated boilerplate code.

This PR contains the following modifications:

• Protocol class now allows passing the parameters through the constructor instead of class variable
• All of the Capability classes retrieve their parameters through protocol.parameters upon initialization (No need to set topics_glob class variables) and use instance variables to get them later (e.g. self.topics_glob instead of Advertise.topics_glob).
• The default values are defined in class level and are only overwritten in the instance if protocol.parameters dictionary contains the keys.
• The ROS parameter and cli argument handling in RosbridgeWebsocketNode has been reworked:
  • Added new module constants SERVER_PARAMETERS and PROTOCOL_PARAMETERS that contain parameter name, type, default value and description.
  • Used argparse for parsing cli arguments (less boilerplate code and more user-friendly interface)
  • Made ROS parameters take precedence over cli args (passing cli args modifies the default values for ROS parameters)
  • A single class variable protocol_parameters is set in RosbridgeWebSocket handler, no need to create it on every opened connection
  • Added missing actions_glob parameter

Some changes in behavior:

• Setting Node parameters before opening Protocol won't affect protocol parameters. The dictionary of parameters needs to be passed in the constructor. This is reflected in tests.
• (Opinionated) max_message_size actually has effect now, that is, even when client sets the fragment_size, the actual fragment size is capped to max_message_size value.

What's left to do:

• I need to figure out how the bson parameters are handled, especially the relation between binary_encoder and bson_only_mode.
• Some real life application testing

Even though this is still WIP, I would appreciate a review

[sea-bass]

I won't get to review this for a bit, but have you considered possibly using https://github.com/PickNikRobotics/generate_parameter_library?

Not sure how well this will do with hybrid ROS params and CLI arguments though, but at least may package up your params in a neat struct.

[bjsowa]

I won't get to review this for a bit, but have you considered possibly using https://github.com/PickNikRobotics/generate_parameter_library?

Not sure how well this will do with hybrid ROS params and CLI arguments though, but at least may package up your params in a neat struct.

Might be a good idea. I'll try to figure out whether I can use it together with cli args

[bjsowa]

@sea-bass I looked at the possibility of using generate_parameter_library and IMO it's not worth it. It will only add complexity instead of simplifying it and won't provide any useful features. All of the parameters are read-only (read only once at the start) and don't require any validation. Also it's not possible to retrieve parameter descriptions for cli args before declaring ROS parameters.