`ArchivableEventItem` - Allows events to be archived

[mumby0168]

It might be the case that events might need to be archived and then removed after a period of time.

public class ArchivableEventItem : EventItem
{
     public bool IsArchived { get; set; }
}

This can use the time to live property to mark the event for deletion after a period of time.

There could then be a new method on the IEventStore<TEventItem> something like _eventStore.ArchiveAsync("partitionKeyValue", x => x.Id == "A")