Rename column valid_till_date to valid_until_date

[zaneselvans]

Overview

Renames the field valid_till_date to valid_until_date to avoid using a non-standard abbreviation that only saves 1 letter.

Testing

Will run make pytest-coverage locally.

To-do list

Beta Give feedback

1. Ensure docs build, unit & integration tests, and test coverage pass locally with make pytest-coverage (otherwise the merge queue may reject your PR)
2. For significant ETL changes, ensure the full ETL runs locally
3. For major data coverage & analysis changes, run data validation tests
4. If updating analyses or data processing functions: make sure to update or write data validation tests
5. Update the release notes: reference the PR and related issues.
6. Review the PR yourself and call out any questions or issues you have

[zaneselvans]

Brought this tiny change into #3421