* Add bookmark queue purging and ExecuteWorkflow stimulus
Introduce BookmarkQueuePurgeOptions and ExecuteWorkflowStimulus classes for managing workflow queue purging and stimulus handling. Implement related handler and activity modifications to support waiting for child workflows and purging old bookmark queue entries.
* Update activity reference in XML comments
Corrected the activity reference from DispatchWorkflow to ExecuteWorkflow in XML comments to accurately reflect the functionality. This change ensures the comments are aligned with the actual code behavior.
* Add bookmark queue purger functionality
Introduce a new class `DefaultBookmarkQueuePurger` to purge old bookmark queue items. This includes an interface `IBookmarkQueuePurger` and a recurring task `PurgeBookmarkQueueRecurringTask`, with necessary updates to `IBookmarkQueueStore` implementations and application configuration.
* Update purging logic in DefaultBookmarkQueuePurger
Refactor the purging operation to use a threshold date for clarity. This includes updating log messages and filter creation to enhance readability and maintainability.
