Add `source` entry for ros2_openai_server (humble)

[AndyZe]

This is a new package so I'm adding the source entry per https://docs.ros.org/en/humble/How-To-Guides/Releasing/Release-Team-Repository.html#create-a-new-release-repository

@brettpac @yassiezar

[marcoag]

Let's discuss in https://github.com/ros/rosdistro/pull/42014.