port SNAX workflow to use OSG workflow API

gstlal-burst/bin/Makefile.am

gstlal-burst/bin/gstlal_snax_extract

gstlal-burst/bin/gstlal_snax_workflow

gstlal-burst/configure.ac

gstlal-burst/python/snax/Makefile.am

gstlal-burst/python/snax/config.py

gstlal-burst/python/snax/dags/Makefile.am

gstlal-burst/python/snax/dags/__init__.py

gstlal-burst/python/snax/dags/layers.py

gstlal-burst/python/snax/feature_extractor.py

gstlal-burst/python/snax/multichannel_datasource.py