Write pytest and ctest extensions that will help start the router in CI jobs

[Yadunund]

The road to Tier-1 status includes passing all nightly CI jobs that run for all core ROS packages.

While we could setup the environment to run without the zenohd router and have nodes discover each other over multicast, it would mean we test with rmw_zenoh in a different configuration that the default behavior.

@cottsay recommended writing extensions for pytest and ctest that can start the zenohd router in a separate process. Also, multiple packages are tested in parallel on the same host in isolated environments and hence the extension would also need to generate router and sessions configs on the fly such that a new system port is assigned to the new router (and the session is notified) as having multiple zenohd routers start with the default config will lead to errors as they will try to bind to the same port.