Automatically select available port for session and launch_session

[isaacwaldron]

📝 Description of the feature

If the default port 50051 is not available, launch_session with port_num=None will fail to launch a session. Instead, it could search for an available port and launch the session there. The same logic could be applied to session to allow port_num=None there as well.

💡 Steps for implementing the feature

1. Implement a test that demonstrates the failure described above.
2. Implement a function find_available_port that finds an open port on localhost to open a listening socket on and returns the port number
3. Modify launch_session and session to call find_available_port when port_num=None

🔗 Useful links and references

No response