Support for custom log levels

[dadrus]

I'm using zerolog to log both regular events, and access log events using two separately configured loggers. I would like to be able to filter these events in the resulted logs easily and thinking about something like a custom log level, e.g. ACCESS. I'm wondering if introducing an option to define custom log levels, like e.g. possible with slog is something you would consider as a valuable extension. Having a new log level named ACCESS or similar for the abovesaid purpose would be fully sufficient as well.