Initialize the appender based on the options set
This is part of the IOptionHandler delayed object activation scheme. The ActivateOptions method must be called on this object after the configuration properties have been set. Until ActivateOptions is called this object is in an undefined state and must not be used.
If any of the configuration properties are modified then ActivateOptions must be called again.
Sets initial conditions including date/time roll over information, first check, scheduledFilename, and calls ExistingInit to initialize the current number of backups.