Support BigQuery DML in BigQueryIO.Write

Since 2016 it's possible to use DML functionality in BigQuery when using standard SQL. It would be great to also support this in Beam. Analogous to BigQueryIO.Read::fromQuery maybe a BigQueryIO.Write::withQuery method can be added, which is supported when standard SQL is enabled?

The reason why I think this is a major issue: within a few months GDPR goes into effect in the EU. This law enforces companies to support deleting all data from a certain customer. I think this feature would be useful in order to automate the deletion/fuzzing process of personal customer data.

Imported from Jira [BEAM-3313](https://issues.apache.org/jira/browse/BEAM-3313). Original Jira may contain additional context.
Reported by: wardva.

Start with the BigQueryIO.Write API and compare it with BigQueryIO.Read::fromQuery, then review how standard SQL is enabled for BigQuery operations. Done means a write-side withQuery method supports BigQuery DML when standard SQL is enabled, with behavior suitable for the stated deletion and data-fuzzing use case.

Written by the indexing model from the issue text.