added request_disk requirements for dags

HTCondor will require request_disk in the dags starting April 26. The modified files are gstlal/python/dags/layers/io.py, gstlal/python/dags/layers/psd.py, and gstlal-inspiral/python/dags/layers/inspiral.py. This MR added "request_disk": "1GB", to jobs that have "request_cpus": 1, and "request_memory": 2000, , "request_disk": "5GB", to gstlal_inspiral and gstlal_inspiral_inj jobs, and "request_disk": "2GB", to the other jobs.