update pudl_out to integrate EIA 923 YTD

[cmgosnell]

The main issue with integrating truly monthly data from YTD sources is in aggregating. If we have only a quarter of data and freq="AS" in a pudl.output.pudltabl.PudlTabl object, then we need to do something to either have truly comparable annual data with the YTD months vs whole years.... or we make this an unacceptable behavior.

The later is my preference for now for a few reasons:

• if we got the aggregation to look year-like, comparing partial years to full years of electricity data is generally incorrect. There is so much seasonable variability. If one were trying to compare the first few months of year A to year B, the more accurate thing to do would be to compare the first few months of year A to the first few months of year B.
• honestly, speed. I'd like to get this integrated quickly and it would be pretty simple to raise a flag if someone was trying to aggregate in a bad way. I'd like to do a more nuanced version of outputs that properly examines YTD data, but this seems like a good interim solution.

[e-belfer]

I think this was resolved in #2902 and can be closed. Thoughts, @cmgosnell ?