expert: add BQ table knowledge to the agent #5344
Description
One-liner
Let's make Expert aware of BQ tables, so that it can answer questions in that domain too.
Background
Currently, Expert knows our semantic layer, by extracting it from our db_docs.yaml file. This file also contains BQ documentation, which Expert could leverage.
https://github.com/owid/analytics/pull/618 is adding some more bits of documentation that were missing.
For more prior context, refer to https://github.com/owid/analytics/issues/465