No parameter available to specify a jobId to Table.upload_from_file()

[mackenzieATA]

There is no way to send a jobId to the upload_from_file function.

My motivation is that I've had issues with uploading the same file twice, duplicating data in the target table. A suggested solution was to specify my own jobId as a hash of the file contents. That way, duplicate uploads would be rejected as having the same jobId. Without modifying the library, there is no ability to do this.

[tseaver]

This should be pretty straightforward:

• Update Table.upload_from_file to take an optional job_name property and pass it through to _configure_job_metadata, along with the table's project.
• Update _configure_job_metadata to set the top-level jobReference IFF the job_name is not None.
• Add test coverage.