Add journal scraper to monitor warnings and errors from the log.

[ghost]

Currently, issues can happen in the pricenode and we may be unaware of them. For example here we observed a Stack Overflow error that was previously unknown. It was only detected by seeing that prices were different on one node.

Pricenode already has one journal scraper which reports bisq version numbers to the monitor.

I propose a similar script (or addition to the existing) can report warnings and errors, so we can know when and how frequently problems occur. Otherwise we are largely in the dark.