document query version control best practice

[maxheld83]

This is about versioning the queries, and by extension, the BigQuery views.

This requires:

• [ ] some github action to trigger a rebuild of views based on a commit
• [ ] settings on bigquery that (at least) some views can only ever be changed by github actions
• [ ] sha-names of views

Many people say this is a good idea:

• https://robertsahlin.com/automatic-builds-and-version-control-of-your-bigquery-views/
• https://web.superquery.io/version-control-bigquery/
• https://caitlinhudon.com/2018/11/28/git-sql-together/