First hacky implementation of reusing the initial_positions for view_ur

[fmauch]

As we have the config file in place already, anyway, we can also use the parameters.

There are a couple of things I don't like about this implementation:

• Parsing the yaml file manually seems awkward to me. However, as far as I understood, passing parameter files to nodes only supports yaml files following a certain syntax, which the initial_positions.yaml is not. (See possible workaround 1)
• I could not manage to make the actual filename configurable as using a LaunchConfiguration object. But that might just be me being stupid.

Possible workaround 1: Include separate file
With defining a separate file with content

joint_state_publisher:
  ros__parameters:
    zeros:
      shoulder_pan_joint: 0.0
      shoulder_lift_joint: -1.57
      elbow_joint: 0.0
      wrist_1_joint: -1.57
      wrist_2_joint: 0.0
      wrist_3_joint: 0.0

we could pass that file to the node directly. However, this would be config duplication.

As I couldn't come up with a better solution, I postet a question on ROS answers: https://answers.ros.org/question/396653/ros2-python-launchfile-load-parametersyaml-into-nodes-parameter/

[fmauch]

I've actually found that pattern in the industrial-training

[destogl]

I don't like much this direct dependency on yaml.

Can we do something like in Driver#308

[destogl]

I would prefer to keep this "multi-row" because it is easier to read and add nodes if needed. I expect people to copy-paste and extend this file.