Add make command for generating backfill configs

[natemcintosh]

Goal

Add a python script, called in a make command to generate configs over multiple report dates.

Context

Now that we want to run backfill tests over multiple report dates, it would be nice to have a way to generate the necessary configs, and then kick off the tasks in Batch all from the Makefile.

Required

• Write a python script, in the manner of generate_configs.py for calling generate_backfill_config().
• Write a make command for calling the script with sensible defaults.

Related

• Add multi report dates cfa-config-generator#63