document and implement changes to the BigQuery schema

[spencerschrock]

Right now, there are two breaking changes to the JSON output that would affect the upload step of our weekly scan infrastructure.

1. Maintainer annotations, which got merged in ⚠️ Add initial Maintainers Annotation parsing #3905 without modifying cron/internal/format/json.go
2. Adding a check ID in ✨ Add check ID #4021 , which currently does touch its cron/internal/format/json.go

This results in a few required steps:

• document the steps these kind of changes required and flag them in our CI
• make the required schema change to support both of these in the BQ table
• wait on ✨ Add check ID #4021 or merge without the changes to cron/internal/format/json.go

[spencerschrock]

cc @ashearin regarding #4021, if you want to merge partially or wait.