BigQuery Denormalized Destination: Support for Date/Datetime types through the format annotation

[cptjacky]

Tell us about the problem you're trying to solve

Trying to load dates columns in BigQuery using the BigQuery Denormalized Destination.

Describe the solution you’d like

When using the BigQuery Denormalized Destination, the generated schema should support the date/datetime types when possible (using the "format" key in the json spec).

Describe the alternative you’ve considered or used

I patched the destination

Additional context

Parsing dates on the fly is costly and I would like to avoid intermediate ("raw") tables in BigQuery to limit storage costs.

Are you willing to submit a PR?

Yes! I will be making a proposal shortly!