Support BigQuery Load jobs for batch loading

[RustedBones]

From beam documentation

When you specify load jobs as the insertion method using BigQueryIO.write().withMethod(FILE_LOADS).

Scio should also give users the possibility to use files to load data to BigQuery

[brucearctor]

@RustedBones -- not sure I understand your issue here.

Is there something you are trying to do that you are not able to ( asking about functionality, not specific syntax/methods ).

[brucearctor]

Ah, based on your other issue ( https://github.com/spotify/scio/issues/4333 ), it looks like you're thinking Scio would benefit from BeamIO.Write Methods --> https://beam.apache.org/releases/javadoc/current/org/apache/beam/sdk/io/gcp/bigquery/BigQueryIO.Write.Method.html ?

[RustedBones]

That's correct. At the moment those are not exposed in the Scio API. Both tickets have been opened after user's request, feel free to assign yourself if you want to work on them.

[brucearctor]

I will need to dig into specifics a bit more -- as don't want to assign myself, until sure that have the ability to see it through relatively quickly ( to not be a holdup/blocker )