This Task will purge errors (in the ^ERRORS global) that are older than the configured value.
It also renames the messages.log file if it is larger than the configured maximum size.
On a MultiValue system it also renames the mv.log file if it grows too large.
This Task is normally run nightly.
This defines the user-visible name of this task; This is defined in subclasses.
This method is responsible for executing the task.
At the scheduled time, the Task Manager creates an instance of this object, sets any property values using the stored "settings" for the task, and then invokes this method to execute the task.