Continue watching for new members in the search client pool if an error can arise

[fmassot]

In the search pool client, we update the pool with new cluster clients in a tokio task.

An error can happen in the task, and the update will stop. We should probably log the error and continue to watch the members channel.

https://github.com/quickwit-oss/quickwit/blob/main/quickwit-search/src/search_client_pool.rs#L181-L183