fix: Improve settings changing

[Koenkk]

Requires #22619, therefore only review the following commit

This PR improves various aspect of changing settings:

• Fix log_syslog always being added to the configuration.yaml when pressing save on the frontend Advanced page
• Settings can now properly be removed (when publishing a null value). Required for e.g. removing log_namespaced_levels entries
• Remove complex settings changing logic by modifying the frontend to only send the diff (requires fix(settings): send settings diff to Z2M instead of whole object nurikk/zigbee2mqtt-frontend#2023)