[Feature Request]: BigQuery input needs support for RECORD data type

### What would you like to happen?

When querying tabes in the Beam BigQuery Input transform, it's not possible to detect or query fields of type RECORD. It would be nice if Hop handled these nested fields with more grace. One possibility would be to give back the record fields as JSON strings.

### Issue Priority

Priority: 3

### Issue Component

Component: Beam

Start at the Beam BigQuery Input transform and inspect how BigQuery schemas and fields are detected and queried. Determine how RECORD fields should be represented, then add coverage showing that nested fields can be queried and handled consistently, with JSON strings as one proposed output.

Written by the indexing model from the issue text.