Ticket 49099 - ns workers prep
    
    Bug Description:  We wish to move to nunc-stans to control our worker
    threads and async tasks.
    
    Fix Description:  This first patch moves the NS worker pool
    creation to main.c, which makes it accesible to both offline
    and online jobs. As well, we no longer "support" a server without
    nunc-stans so remove the configure options. We still allow enable
    disable of the feature however, so this has been fully tested.
    
    https://pagure.io/389-ds-base/issue/49099
    
    Author: wibrown
    
    Review by: mreynolds (thanks!)