[Feature Request]: document BigQuery CDC record format #39768

What would you like to happen?

I was attempting to use the Python SDK to work with the BigQuery IO connector to send Change Data Capture records to BigQuery. It seems that BigQuery has a special format for receiving CDC records and the Beam implementation understands this format. However there are special flags that need to be set and the input PCollection records have to be a special format. I was able to decode this after much pain by looking at the source code. This issue asks for these to be captured in documentation ... ideally here.

Issue Priority

Priority: 2 (default / most feature requests should be filed as P2)

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