[WIP] Add draft of RUS-EIA crosswalk

[e-belfer]

Overview

What problem does this address?

This covers the first step of #5166, by checking in the original provided crosswalk spreadsheet into our glue package data.

What did you change?

Added the spreadsheet to the package_data/glue module, renaming column headers from the source file to reflect variable names used in PUDL.

Documentation

Make sure to update relevant aspects of the documentation:

• Update the release notes: reference the PR and related issues.
• Update relevant Data Source jinja templates (see docs/data_sources/templates).
• Update relevant table or source description metadata (see src/metadata).
• Review and update any other aspects of the documentation that might be affected by this PR.

Testing

How did you make sure this worked? How can a reviewer verify this?

To-do list

• Review the PR yourself and call out any questions or issues you have.

[cmgosnell]

i'll add a "real" review shortly but let's just scope this as merging the file into main and talk about next steps of integration after the fact