[2.4.0] Checkmk Werk 16566 created: Standardize notification spooler log level configuration

[//]: # (werk v2) # Standardize notification spooler log level configuration key | value ---------- | --- date | 2024-09-02T09:16:08+00:00 version | 2.4.0b1 class | fix edition | cee component | notifications level | 2 compatible | yes The notification spoolers log level was configured differently than other services. Previously users had the choice between: * Normal logging (only startup, shutdown and errors) * Verbose logging (also spooled notifications) * Debugging (log every single action) This was changed to the standard log levels which we also use in all other services. The command line flag `-v` of the `mknotifyd`, which could be used to override the configured log level was replaced with the `--log-level=LEVEL` argument. While the change to this command line flag is an incompatible change, we don't rate this as a change that is worth marking the werk to be incompatible. In the end it's only an option used for manual debugging.