Add support for extra custom time zone resolver function in TimeZoneUtil

[RFlipper]

I use the following code to schedule a job:

var webTimezoneOffset = TimeSpan.FromMilliseconds(task.WebTimezoneOffset);
var webTimezone = TimeZoneInfo.CreateCustomTimeZone("Current Web Timezone", webTimezoneOffset, null, null);

var trigger = TriggerBuilder.Create()
                .WithIdentity(task.TaskId.ToString())
                .WithCronSchedule(task.CronExpression, t => t.InTimeZone(webTimezone))
                .StartAt(task.StartTime - new TimeSpan(0, 0, 1))
                .Build();

In that case I get the following error:

Quartz.JobPersistenceException: Couldn't retrieve trigger: The time zone ID 'Current Web Timezone' was not found on the local computer. ---> System.TimeZoneNotFoundException: The time zone ID 'Current Web Timezone' was not found on the local computer.
   at System.TimeZoneInfo.FindSystemTimeZoneById(String id)
   at Quartz.Util.TimeZoneUtil.FindTimeZoneById(String id) in c:\Program Files (x86)\Jenkins\workspace\Quartz.NET\src\Quartz\Util\TimeZoneUtil.cs:line 110

As I researched the issue in method LoadExtendedTriggerProperties in the file https://github.com/quartznet/quartznet/blob/045344fe21cbdb2229cb6ac496652941a275e61b/src/Quartz/Impl/AdoJobStore/CronTriggerPersistenceDelegate.cs

I wonder to know if it possible to add support saving time zone offset.

[lahma]

I know this won't fully cover the use case, but opens some possibilities:

// custom time zone
const string CustomTimeZoneId = "Custom TimeZone";
var webTimezone = TimeZoneInfo.CreateCustomTimeZone(
	CustomTimeZoneId, 
	TimeSpan.FromMinutes(22),
	null, 
	null);

TimeZoneUtil.CustomResolver = id =>
{
	if (id == CustomTimeZoneId)
	{
		return webTimezone;
	}
	return null;
};

var customTimeZoneTrigger = TriggerBuilder.Create()
	.WithIdentity("customTimeZoneTrigger")
	.WithCronSchedule("0/5 * * * * ?", x => x.InTimeZone(webTimezone))
	.StartNow()
	.ForJob(job)
	.Build();

scheduler.ScheduleJob(customTimeZoneTrigger);
var loadedCustomTimeZoneTrigger = (ICronTrigger) scheduler.GetTrigger(customTimeZoneTrigger.Key);
Assert.That(loadedCustomTimeZoneTrigger.TimeZone.BaseUtcOffset, Is.EqualTo(TimeSpan.FromMinutes(22)));

Only having offset isn't enough as daylight savings vary by time zone id. This means requiring to encode offset to name in your case.