Fix merge CLI command.

[fmassot]

Fix #2062 and partially #1981

Partially because the logs end up like this:

2022-10-19T18:45:18.936Z  INFO quickwit_actors::spawn_builder: actor-exit actor_id=IndexingPipeline-twilight-8Ygs exit_status=Success
2022-10-19T18:45:18.938Z  INFO quickwit_actors::spawn_builder: actor-exit actor_id=quickwit_indexing::actors::indexing_service::IndexingService-blue-Swh0 exit_status=Quit
2022-10-19T18:45:18.938Z ERROR quickwit_actors::actor: actor-failure actor_name="quickwit_indexing::actors::indexing_service::IndexingService-blue-Swh0" actor_exit_status=Quit
2022-10-19T18:45:19.939Z  INFO quickwit_actors::spawn_builder: actor-exit actor_id=Scheduler-icy-gsOt exit_status=Killed
2022-10-19T18:45:19.939Z ERROR quickwit_actors::actor: actor-failure actor_name="Scheduler-icy-gsOt" actor_exit_status=Killed

We don't want ERROR logs when everything goes well. I think we should not print an ERROR on an "actor_handle.quit()".

I opened an issue to see what we can do on that #2150.