Refactor `build_demand.py` to use EIA930 data from PUDL

Feature Request

Catalyst Coop is currently in the midst of adding EIA930 data to PUDL.

They just produced their first nightly build that includes (relatively unprocessed) hourly EIA-930 balancing authority operations data, including the following 4 tables:

• core_eia930__hourly_interchange
• core_eia930__hourly_net_generation_by_energy_source
• core_eia930__hourly_operations
• core_eia930__hourly_subregion_demand

Docs are here, notebook poking at the data here.

Once the tables graduate to out_eia930_*, meaning they have been fully cleaned up and are production ready, we'll need to refactor build_demand to pull EIA930 data from PUDL.

Suggested Solution

• Identify which PUDL tables / columns we need
• Check in with Zane from Catalyst about when out versions of the data will be out
• Refactor workflow/scripts/building_demand.py to query tables for data
• Update Snakefile to make build_demand task depend on forthcoming retrieve_pudl task (#311)

Start by reading the linked PUDL EIA930 documentation and sanity-check notebook, then inspect workflow/scripts/building_demand.py and the Snakefile. Identify the required PUDL tables and columns, confirm that the out_eia930 data is production-ready, and trace the dependency on the forthcoming retrieve_pudl task. Done means build_demand uses the cleaned PUDL data and the workflow dependency is updated.