MicrosoftILoggerTarget - Add support for override LoggerName when using ILoggerFactory

[snakefoot]

Then output from NLog Loggers can be redirected to match function-name:

//setup target to forward NLog logs to ILogger
//NOTE: string passed to CreateLogger must match "function.<function name>" or logs will not show in Log Stream
var msLoggerFactory = serviceProvider.GetService<ILoggerFactory>();
var msLogger = msLoggerFactory.CreateLogger("Function.TestLog");
var nLogToMsLogTarget = new MicrosoftILoggerTarget(msLogger) { LoggerName = "${mdlc:FunctionName}" };

And one can then forward the ILogger-name to NLog like this:

    [FunctionName("TestLog")]
    public static async Task<IActionResult> TestLog([HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)]
                                                HttpRequest req, ILogger log)
    {
        using (NLog.MappedDiagnosticsLogicalContext.SetScoped("FunctionName", log.ToString()))
        {
           //shows in both Application Insights and Log Stream.
           log.LogInformation("Log From ILogger");

           //shows in Application Insights but not in Log Stream.
           _logger.Info("Log From NLog");

           return new OkObjectResult("OK");
        }
    }

See also: https://stackoverflow.com/questions/66357471/nlog-in-azure-function-log-streams-using-nlog-config