Implement `attach_job` method on BigQuery Query Client

[alvarowolfx]

Allow to get a Query handle from an existing query job.

impl BigQuery {
    /// Re-attach hook to bind an existing out-of-process job reference.
    pub async fn attach_job(
       &self,
       job_ref: google_cloud_bigquery_v2::model::JobReference,
    ) -> Result<Query>;
}