Change logging configuration section to support relative paths & other options

[Geod24]

Currently out LoggerConfig is just for one logger, but we can't set "wide" logging option.
Suggestion:

public struct LoggingConfig
{
    /// Directory used for relative paths in `LoggerConfig.file`
    public string directory = "logs";
    
    /// Whether to use per-client file for the network manager
    public bool segment_file_per_client = false;

    /// Per logger config
    @Key("name")
    public immutable(LoggerConfig)[] loggers = [ {
        name: null,
	level: LogLevel.Info,
        propagate: true,
        console: true,
        additive: true,
    } ];
}

Note that an absolute path in loggers is still treated like an absolute path.