Move stagingLocation and tempLocation to GcsOptions

[peihe]

This will allow BigQueryOptions to extend GcsOptions, and BigQueryIO can access them through BigQueryOptions.

[peihe]

R: @lukecwik @dhalperi

[davorbonaci]

Hm... Can you argue more why this is the right change?

GcsOptions should be about accessing GCS itself, but not necessarily job-wide settings like stagingLocation. Also, it is unclear that there's no a converse case -- where somebody could benefit from this actually being in DataflowPipelineOptions.

[peihe]

The reason is BigQueryIO needs a tempLocation option across runners.
The issue is the default value of tempLocation is coming from stagingLocation.
That is why I pull both of them to GcsOptions.

Another option is to pull both of them to a new PipelineOption.

[davorbonaci]

Sounds like we might need a job-wide temporary location. I think this needs some discussion.

[dhalperi]

This one is tough -- the tempLocation here needs to be a GCS bucket -- BigQuery can only export/import to/from GCS. So this needs to be runner-independent (can't use DataflowPipelineOptions.getLempLocation()) but needs to be GCS/GCP/BigQuery specific.

Would be nice to be able to reuse the one from DataflowPipelineOptions if such exists.