Harmonize logback threshold and pekko logLevel

[t-ober]

Currently the log threshold is set via a filter that is configured in resources/logback.xml.
Furthermore we have a logLevel configuration in pekko.conf which is inculded in the "regular" simona configuration.
Having two (possibly conflicting) log level settings is not ideal.
It would be better to stick with only having to configure the log level via the regular configuration file and get rid of the filter in the logback configuration.

[sebastian-peter]

Hmm. In general, I agree that this is confusing. But also I think it'd make sense to have separate log levels for logs generated by pekko (might only be interested in logs beyond WARN) and SIMONA logs (might be interested in DEBUG, or at least INFO)

[sebastian-peter]

Marius and I simplified the situation a little bit with #1026, so that the log level of the output file can be configured via simona config file. Pekko log levels are still configured via pekko.conf, but as I argued above, I would keep it this way.

The last thing that might be a bit annoying is that you still set the console log level via logback.xml. We might want to migrate that configuration into simona config as well.