Mount GCP credentials in local docker environments.

[robertwb]

This allows cross-langauge transforms, such as IOs, to authenticate
as if they were running in process.

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[robertwb]

R: @johnjcasey

[codecov]

Codecov Report

Merging #19265 (be4d0c3) into master (f24cedf) will decrease coverage by 0.01%.
The diff coverage is 8.33%.

@@            Coverage Diff             @@
##           master   #19265      +/-   ##
==========================================
- Coverage   74.07%   74.05%   -0.02%     
==========================================
  Files         697      697              
  Lines       91927    91939      +12     
==========================================
- Hits        68092    68086       -6     
- Misses      22590    22608      +18     
  Partials     1245     1245              

Flag	Coverage Δ
python	83.71% <8.33%> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
...nners/portability/fn_api_runner/worker_handlers.py	77.89% <8.33%> (-1.45%)	⬇️
sdks/python/apache_beam/internal/gcp/auth.py	73.33% <0.00%> (-5.34%)	⬇️
.../apache_beam/runners/interactive/dataproc/types.py	93.10% <0.00%> (-3.45%)	⬇️
sdks/python/apache_beam/internal/dill_pickler.py	84.89% <0.00%> (-1.44%)	⬇️
sdks/python/apache_beam/transforms/core.py	92.14% <0.00%> (-0.16%)	⬇️
sdks/python/apache_beam/coders/coders.py	88.22% <0.00%> (-0.13%)	⬇️
sdks/python/apache_beam/ml/inference/pytorch.py
...thon/apache_beam/ml/inference/pytorch_inference.py	0.00% <0.00%> (ø)
...hon/apache_beam/runners/worker/bundle_processor.py	93.54% <0.00%> (+0.24%)	⬆️
...hon/apache_beam/runners/direct/test_stream_impl.py	94.02% <0.00%> (+0.74%)	⬆️

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[johnjcasey]

Is there a way to test this?

[robertwb]

I've tested this manually, but there doesn't seem a good way to meaningfully unit test this. It will be depended on by some future cross-language tests though.

[johnjcasey]

Thats sort of what I thought. LGTM, and lets just keep an eye on this until those xlang tests are set up