Feature request: Better handling of corrupted database

[marcinstrzelczyk]

Hello,
I've experienced mosquitto database corruption which I've described in #3159.

In this issue I would like to focus on how mosquitto handles the corrupted database.

Right now it logs the error and exits, which for me is much worse than the corrupted database itself. I could live with very rare data loss, but if mosquitto fails to start, that's a much bigger problem.

For me it would be much better if mosquitto started with an empty database, if the existing one becomes corrupted. Would it be possible to implement such behavior? It could be configurable in mosquitto.conf to support both existing behavior and the new one.