Add ability for WMS-specific default configs

For automatic memory scaling to work in ctrl_bps_htcondor, memoryLimit must be set. Normally, it should reflect the actual limitations of the computational resource (e.g. the largest memory value among available HTCondor execution points). However, at SLAC there’s no native HTCodnor execution points as they are created dynamically using glideins governed by allocateNodes.py. As allocateNodes.py --auto is able to adjust memory requirements for the glideins based on the memory requirements of the jobs in the HTCondor job queue in order to enable using automatic memory scaling it should be sufficient to provide a default value for memoryLimit. The goal is to include a YAML file that will provide a default value for this parameter in ctrl_bps_htcondor as well as making any changes so it can be set as any other BPS parameter (in decreasing order of priority):

1. as a command line option,

2. in the user’s BPS config,

3. in plugin’s defaults,

4. in BPS defaults.