Adding ability to give default QueryJobConfig to Client

[blainehansen]

closes #5183

This isn't a complete request (I need to do things like fill out the Contributor License Agreements, get coverage all the way to 100%, etc), but I wanted to begin the discussion to see if this was an acceptable direction. Only QueryJobConfig has been implemented, but the other types shouldn't be too difficult, since I've added a _JobConfig.fill_from_default method.

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CLAs look good, thanks!

[tseaver]

@blainehansen

Making a PR from your master branch makes things hard for you over the long term: it creates barriers to synchronizing with this repository's master over time.

WRT the test failures, there is missing line / branch coverage for:

google/cloud/bigquery/client.py               374      1    160      1    99%   1244, 1236->1244

which is the case where no job_config is passed.

[blainehansen]

@tseaver Sorry about not creating a feature branch ha, I don't expect to maintain a fork for a long period, I was just hoping to include this feature, but I shouldn't have cut corners.

[tswast]

Looking good, thanks! Just a few comments. I'm not convinced we need the merge_job_config argument yet.

[tswast]

Love it! Thank you so much for your contribution, @blainehansen.

FYI: I've made fill_from_default "private" by prefixing an underscore, because I don't think it's necessary to add this method to the public API interface. (It's fine to use from other modules within this library.)

@tseaver Please take a look.

[blainehansen]

👍 yeah making that private is definitely a better choice 😄

[blainehansen]

🎊 🎊 🎊

Thanks everyone!