[BEAM-8275, BEAM-8428] Update SQL BigQuery doc

[11moon11]

BigQueryTable now:

• Can accept TBLPROPERTIES
• Perform project and predicate push-down when method is set to DIRECT_READ

Documentation should reflect that. Added missing commas and fixed typos.

R: @apilloud
CC: @TheNeuralBit
CC: @amaliujia

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