Feature request

Feature description

Provide a standard interface for parsing parameters from yaml files to avoid code duplication.

Loading a parameter file is something extremely common in ROS1. In ROS2 it's possible as part of a Node launch_ros action. I also made a PR to add it as a ros2 param verb: ros2/ros2cli#590

In the future there will be more situations where this is needed, and it's not straightforward because of wildcard node names and nested parameters. Another use case here. Also I believe there should be a launch_ros action that allows to load parameters on an existing node.

So there are already 2 implementations of loading a yaml file, and soon will be more unless we put this code somewhere.

Implementation considerations

Could we add it to https://github.com/ros2/rclpy/blob/master/rclpy/rclpy/parameter.py ?
At least the part of parsing a yaml file + node name into an array of ParameterMsg.

Might be interesting of implementing the dumping functionality from ros2 param dump here as well.