Support Map in BQ for StorageWrites API for Beam Rows

[prodriguezdefino]

Currently, BigQuery table schema utility and the implementation for StorageWrites for Beam Rows does not support sending rows with properties of type Map or array of Map as part of their schema.

This PR adds that functionality transforming the Map into a Message type which contains two fields, key and value, respecting the types coming from the Row schema while mimicking the behavior when using TableRows to the BigQueryIO PTransform.

Copied from #22179 since it got closed after inactivity for long period (and I can not re-open it).

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