Optionally exit pipeline when exiting client

[MaxiBoether]

Sometimes, when running the modyn-client, I want to abort the current pipeline. However, since it is executed at the supervisor, this is not possible. One solution is to kill the container, but this stops all running pipelines, which interferes with other running experiments. Hence, it would be good, when CTRL+C'ing the modyn-client, to send some form of interrupt to the supervisor, who then takes care of exiting the pipeline gracefully. However, sometimes we also just want to let the modyn-client exit but not the pipeline, so there should be some form of "Do you want to exit the pipeline as well (y/n)?"