Update 176 and ATB archivers to not hardcode year

[e-belfer]

Overview

Addresses part of #372.

What problem does this address?
With hardcoded years, we currently have to remember to check whether a new year of data is out. The monthly archiver runs won't capture new years of data released.

What did you change in this PR?
Removes hardcoded year from NREL ATB and EIA 176 archivers.

Testing

How did you make sure this worked? How can a reviewer verify this?
Run both archivers. Verify all years expected to download are successfully downloaded.

To-do list

Tasks

Beta Give feedback

1. Update relevant documentation - like comments, docstrings, README, release notes, etc.
2. Review the PR yourself and call out any questions or issues you have

[zaneselvans]

• Request for a bit more info in docstring.
• Question about maybe a variable name that needs to be updated?