Emit maintenance daemon's logs to a different file than the server log

The maintenance daemon runs as a background worker and executes some tasks periodically including distributed deadlock detection, basic statistic collection and 2PC recovery (soon to be merged).

Currently, the logs of these operations are also sent to the PostgreSQL's server log. It might make sense to use a different log file for these purposes given that the daemon might produce lots of logs, and this could confuse the users.

We might even consider using separate files for each of the tasks in the daemon (but not sure if that's a good idea just noting for reference 😄 )