Develop shapefiles for balancing authority regions and sub-regions

# :rocket:

- [x] Is your feature request essential for your project?

### Describe the workflow you want to enable
I wish I had a shapefile that contained geometries for as many of the contiguous U.S. balancing authority regions and sub-regions as possible. The ideal set of regions and sub-regions includes all those present in the dataset at https://zenodo.org/record/4116342.

### Describe alternatives you've considered, if relevant
- We currently have a rough county-to-BA mapping (see `prereise/gather/data/BA_County_map.json`), but this performs poorly when a county is split between multiple balancing authorities.
- There are datasets within the HIFLD data on [Control Areas](https://hifld-geoplatform.opendata.arcgis.com/datasets/02602aecc68d4e0a90bf65e818155f60_0/about) and [Utility Areas](https://hifld-geoplatform.opendata.arcgis.com/datasets/02602aecc68d4e0a90bf65e818155f60_0/about), but they're mostly county-based as well and have lots of overlap.
- NREL has a map for utilities that may have better granularity, but their labeling leaves a lot to be desired when trying to aggregate back up to balancing authorities. https://maps.nrel.gov/solar-for-all/ (select Electric Utility from the Utilities tab on the left, and then you can download the shapefile).
- Some other scattered data are available publicly, e.g. [NYISO sub-regions](https://www.arcgis.com/home/item.html?id=3a510da542c74537b268657f63dc2ce4) and [CAISO sub-regions](https://cecgis-caenergy.opendata.arcgis.com/apps/CAEnergy::california-electric-infrastructure-app/explore).

### Additional context
It's most important to get the large balancing authorities and their sub-regions correct. Smaller balancing authorities can be merged with larger surrounding balancing authorities as necessary.