Add option to start robot_state_publisher and joint_state_publisher when calling spawn()

[musamarcusso]

When writing tasks using the task_manager submodule, if the SimulationModel instance is added to the running simulation using spawn, sometimes robot_state_publisher and joint_state_publisher also need to be started in order to have the correct tf frames published.
Add the option to also start those nodes, if necessary within the spawn function.