Support Query RPC for fast first page results

BigQuery supports both the InsertJob RPC (with type QueryJob) as well as a Query RPC (https://github.com/googleapis/googleapis/blob/8798ceff3f6fbcdce3186b67ce9339df337569d5/google/cloud/bigquery/v2/job.proto#L117). InsertJob is an asynchronous RPC stores the query results in a BigQuery table, while Query is a synchronous RPC that returns the first page of results immediately while executing a QueryJob asynchronous for the rest of the results.

Add a Query method that returns the first page of results as a collection of std::tuples and a JobReference that can be used to poll for the remainder of the results.

Start by reviewing the existing InsertJob and QueryJob handling, then read the linked BigQuery job.proto Query RPC definition. Add a Query method that returns the first page as std::tuples and a JobReference for polling the remaining results; completion should be demonstrated by tests covering both returned values.

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