[Feature Request]: WriteToParquet schema as side input

### What would you like to happen?

We have a need to pass a dynamic schema to the WriteToParquet PTransform but it will not accept a side input in the schema arg. Would this be possible to implement? My thought is that a similar approach to the WriteToBigQuery PTransform could be used.

### Issue Priority

Priority: 3 (nice-to-have improvement)

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