BigQuery: support labels field of Datasets and Table resources

[tswast]

Docs (talks about datasets, but tables can have labels, too):
https://cloud.google.com/bigquery/docs/labeling-datasets

API references:
https://cloud.google.com/bigquery/docs/reference/rest/v2/datasets#labels
https://cloud.google.com/bigquery/docs/reference/rest/v2/tables#labels

If the patch request is not yet supported, this will be needed, too.
https://cloud.google.com/bigquery/docs/reference/rest/v2/datasets/patch
https://cloud.google.com/bigquery/docs/reference/rest/v2/tables/patch

[rouzwawi]

Any update on this issue?

We're looking to use the high-level BigQuery client to read labels for datasets. But neither bigquery.listDatasets(...) nor bigquery.getDataset(...) propagate the labels field from low level protobuf types up to Dataset.

I could open a PR as it seems to be a simple fix.

[garrettjonesgoogle]

@rouzwawi we would welcome your contribution for this :-)

[garrettjonesgoogle]

We have a project to prepare BigQuery for GA, and this feature is part of the list (P0 for dataset labels, P2 for table labels). I'm going to close this out and let the feature be tracked internally.