get rid of crab3/CRAB3ServerConfig

[belforte]

as discussed in Udine's workshop we will eliminate this directory and stop pulling the external config from glitlab into CRABServer

• "compatible versions" --> remove. Since now we control client distribution via CVMFS we do not have to worry about ancient clients laying around anymore
• "banned-out-destinations" --> remove. A bad idea. And we do not use it
• "htcondorPool": "cmsgwms-collector-global.cern.ch:9620,cmsgwms-collector-global.fnal.gov:9620" --> become part of TW config template in puppet
• cmsweb-shedds-config.json --> become part of TW puppet config as well. Pick each scheduler weight from a hiera variable in each scheduler VM's yaml hiera file
• "modes" --> disappear. Means that in RESTCache.py the S3 bucket name must be chosen based on the "instance" field in the URL used by the client : https://cmsweb..../crabserver/instance/cache?subresource=..... I do not know how to do this yet
• delegate-dn --> needs to stay in the server, so that CRABClient can retrieve and create proper credential. So make it part of CRABServer's config.py (which should be moved out of secrets). Since this file "never changes" we could even make it part of REST container. And if cluster-dependent minor tweaks will ever be needed, use env.vars. set via Helm vaues files
• once all of that is done and verified to work, we can remove the code which loads external configuration in the REST and the files from gitlab