Coordination of `deprecation-date` and table expiration on BigQuery

### Contributions

- [X] I have read the contribution docs, and understand what's expected of me.

### Link to the page on docs.getdbt.com requiring updates

https://docs.getdbt.com/reference/resource-properties/deprecation_date

### What part(s) of the page would you like to see updated?

> setting a model to expire 48 hours after its `deprecation_date`

☝️ Explain how to do this within dbt using the [`datetime`](https://docs.getdbt.com/reference/dbt-jinja-functions/modules#datetime) module

### Additional information

dbt-bigquery can set an [`hours_to_expiration`](/reference/resource-configs/bigquery-configs#controlling-table-expiration) that translates to `expiration_timestamp` within BigQuery.

dbt does not automatically synchronize `deprecation_date` and `hours_to_expiration`, but users may want to coordinate them in some fashion (such as setting a model to expire 48 hours after its `deprecation_date`). Expired tables in BigQuery will be deleted and their storage reclaimed.