run KWS on a separate server

* new benchmark is here: https://github.com/dmwm/DAS/issues/4053
  - looks OK, don't see much impact on DAS UI when running with 4 threads for KWS
  - still the two servers run on different threads, and GIL still applies, so I'd rather limit KWS thread pool to <=4 until we implement load balancing
* it run's DAS and KWS servers on separate ports
  - in current on server production deployment, KWS is proxied in the same way as DAS is: see https://github.com/vidma/deployment/commit/f93526fdaf9e4535f59d8c75d2400c6035bd9a5d
  * so user's browser accesses http://cmsweb.cern.ch/das/kws_async
  - in private development set up, we directly query different port via ajax to get KWS results (see https://github.com/dmwm/DAS/compare/kws-separate-server#diff-2ef4d887ee7faacd0531b9bcc45c1ad1R23)