BigQuery: Decouple clustering from time partitioning when writing

[GStravinsky]

fixes #20673

BigQuery allows to have clustered but not time-partitioned tables. Beam should allow it too.

Used #27097 as a starting point

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[GStravinsky]

retest this please

[GStravinsky]

Run Java_GCP_IO_Direct PreCommit

[GStravinsky]

assign set of reviewers

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[damccorm]

@damondouglas could you please take a look at this one?

[damondouglas]

@GStravinsky Thank you for your contribution! LGTM