[Feature Request]: Support custom avro DatumReader when reading from BigQuery

[kkdoon]

What would you like to happen?

Currently while reading from BigQueryIO, the Beam API internally converts Avro record to Generic record and then users are required to provide conversion functions to convert Generic Record to the final object. However, in some cases It would be more performant to allow users to pass a datumReader implementation that would directly convert the avro data to the final object.

Issue Priority

Priority: 3

Issue Component

Component: io-java-gcp

[kkdoon]

.take-issue .add-labels bigquery, gcp, io

[github-actions]

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