More Configurable Test Play

[kasohrab]

Description

Making an issue again cause it helps me remember to do it eventually.

As we learned from the scrim, configurable params are great.

We should be able to swap between test plays via cli for testing. We already have a python side param client we can use for this or it can just be a gameplay node param since it doesn't need to be shared. At the same time we should resolve #1666. Actually following yagni, let's just make the test play configurable for now.

Requirements

• Can switch between test plays with cli
• Then add this to the UI
• (and other params like plus/minus and other configurable values). <- future pr should do this

Design -- Sources

The design should basically be:
Test play is a gameplay node param string.
Test play is a string topic which the ui will publish to gameplay node.
Must also add a callback to gameplay node to reject test plays if they do not exist in a set of valid plays.
This way we don't pollute global param server when only these two nodes need it. Also it allows the the ui to update with a gameplay node subscription callback.

User can change test play with ui or use cli (ui will just be a wrapper for that ros2 param cli cmd).

https://github.com/ros2/launch/blob/master/launch/launch/actions/opaque_function.py
https://github.com/jrgnicho/collaborative-robotic-sanding/blob/3902e4f0e76bde226b18a997fd60fc30e1961212/crs_application/launch/perception.launch.py#L21
https://docs.ros.org/en/foxy/Tutorials/Using-Parameters-In-A-Class-Python.html#write-the-python-node