Add initial read_gbq wrapper

[svetakvsundhar]

Part of #20810

This PR adds a wrapper function 'read_gbq', that wraps a wrapper PTransform 'ReadGbq'. 'ReadGbq' allows users to Read from BQ, convert the schema into a Beam Schema, and plumb into a Deferred Dataframe.

---

Thank you for your contribution! Follow this checklist to help us incorporate your contribution quickly and easily:

• [x] Choose reviewer(s) and mention them in a comment (R: @username).
• [ ] Mention the appropriate issue in your description (for example: addresses #123), if applicable. This will automatically add a link to the pull request in the issue. If you would like the issue to automatically close on merging the pull request, comment fixes #<ISSUE NUMBER> instead.
• [ ] Update CHANGES.md with noteworthy changes.
• [ ] If this contribution is large, please file an Apache Individual Contributor License Agreement.

See the Contributor Guide for more tips on how to make review process smoother.

To check the build health, please visit https://github.com/apache/beam/blob/master/.test-infra/BUILD_STATUS.md

GitHub Actions Tests Status (on master branch)

See CI.md for more information about GitHub Actions CI.

[codecov[bot]]

Codecov Report

Merging #22616 (3d17f62) into master (720ee14) will increase coverage by 0.02%. The diff coverage is 94.44%.

@@            Coverage Diff             @@
##           master   #22616      +/-   ##
==========================================
+ Coverage   74.23%   74.26%   +0.02%     
==========================================
  Files         707      710       +3     
  Lines       93295    93885     +590     
==========================================
+ Hits        69257    69719     +462     
- Misses      22770    22898     +128     
  Partials     1268     1268              

Flag	Coverage Δ
python	83.57% <94.44%> (-0.05%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
sdks/python/apache_beam/dataframe/io.py	89.53% <94.44%> (+0.75%)	:arrow_up:
sdks/python/apache_beam/typehints/__init__.py	77.77% <0.00%> (-22.23%)	:arrow_down:
.../python/apache_beam/testing/test_stream_service.py	88.09% <0.00%> (-4.77%)	:arrow_down:
...examples/inference/sklearn_mnist_classification.py	43.75% <0.00%> (-3.75%)	:arrow_down:
sdks/python/apache_beam/utils/subprocess_server.py	56.54% <0.00%> (-2.20%)	:arrow_down:
...n/apache_beam/ml/gcp/recommendations_ai_test_it.py	73.46% <0.00%> (-2.05%)	:arrow_down:
...che_beam/runners/interactive/interactive_runner.py	90.06% <0.00%> (-1.33%)	:arrow_down:
sdks/python/apache_beam/runners/direct/executor.py	96.46% <0.00%> (-0.55%)	:arrow_down:
sdks/python/apache_beam/typehints/schemas.py	93.84% <0.00%> (-0.48%)	:arrow_down:
sdks/python/apache_beam/coders/coders.py	88.00% <0.00%> (-0.35%)	:arrow_down:
... and 32 more

:mega: We’re building smart automated test selection to slash your CI/CD build times. Learn more

[github-actions[bot]]

Assigning reviewers. If you would like to opt out of this review, comment assign to next reviewer:

R: @pabloem for label python. R: @johnjcasey for label io.

Available commands:

• stop reviewer notifications - opt out of the automated review tooling
• remind me after tests pass - tag the comment author after tests pass
• waiting on author - shift the attention set back to the author (any comment or push by the author will return the attention set to the reviewers)

The PR bot will only process comments in the main thread (not review comments).

[svetakvsundhar]

R: @TheNeuralBit this is ready for an initial pass, PTAL.

[svetakvsundhar]

Thanks for the suggestions @TheNeuralBit , I think this is ready for another pass.

[svetakvsundhar]

Run Python_PVR_Flink PreCommit

[TheNeuralBit]

Run Python 3.8 PostCommit

[svetakvsundhar]

Run Python 3.8 PostCommit

[svetakvsundhar]

Run Python PreCommit

[svetakvsundhar]

Thanks @TheNeuralBit ! Ive addressed changes, ptal. I've also verified that the new IT's are running.

[svetakvsundhar]

Run Python 3.8 PostCommit

[svetakvsundhar]

thanks! changes made

[svetakvsundhar]

Run Python 3.8 PostCommit

[svetakvsundhar]

Run Python PreCommit

[svetakvsundhar]

@TheNeuralBit ptal and lmk if the io_it_test looks viable

[TheNeuralBit]

Run Python PreCommit

[TheNeuralBit]

@TheNeuralBit ptal and lmk if the io_it_test looks viable

Looks great! I can merge when we get CI green

[svetakvsundhar]

Run Python PreCommit

[svetakvsundhar]

Run Python PreCommit