Use Spark 3 job-server as default Spark job-server for PortableRunner

[mosche]

Use Spark 3 job-server as default Spark job-server for PortableRunner (addresses #23728).

This includes changing Spark runner option --spark_version to use Spark 3 as default.
Besides being deprecated, the Spark 2 runner is in a badly broken state and it's unlikely it's successfully used (#23568).

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[codecov]

Codecov Report

Merging #23751 (7669a0b) into master (3ab9507) will increase coverage by 0.05%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master   #23751      +/-   ##
==========================================
+ Coverage   73.17%   73.22%   +0.05%     
==========================================
  Files         720      720              
  Lines       96044    96279     +235     
==========================================
+ Hits        70278    70505     +227     
- Misses      24454    24462       +8     
  Partials     1312     1312              

Flag	Coverage Δ
python	82.99% <0.00%> (+0.04%)	⬆️

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

Impacted Files	Coverage Δ
...dks/python/apache_beam/options/pipeline_options.py	94.45% <ø> (ø)
...on/apache_beam/runners/portability/spark_runner.py	67.34% <0.00%> (ø)
...m/runners/portability/spark_uber_jar_job_server.py	84.32% <0.00%> (ø)
.../python/apache_beam/testing/test_stream_service.py	88.09% <0.00%> (-4.77%)	⬇️
sdks/python/apache_beam/ml/gcp/visionml_test_it.py	63.63% <0.00%> (-3.04%)	⬇️
...che_beam/runners/interactive/interactive_runner.py	90.50% <0.00%> (-1.27%)	⬇️
sdks/python/apache_beam/coders/coders.py	87.48% <0.00%> (+0.12%)	⬆️
...hon/apache_beam/runners/worker/bundle_processor.py	93.67% <0.00%> (+0.12%)	⬆️
sdks/python/apache_beam/io/gcp/gcsio.py	94.25% <0.00%> (+1.99%)	⬆️
sdks/python/apache_beam/ml/gcp/visionml.py	95.23% <0.00%> (+2.64%)	⬆️
... and 1 more

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[mosche]

Run Java PreCommit

[mosche]

Run Java_Examples_Dataflow PreCommit

[mosche]

Run Python PreCommit

[damccorm]

Run Java_Examples_Dataflow PreCommit

[damccorm]

Run Python_PVR_Flink PreCommit

[damccorm]

Run Seed Job

[damccorm]

Run Go Spark ValidatesRunner

[damccorm]

Run Java Spark PortableValidatesRunner Batch

[damccorm]

Run Python Spark ValidatesRunner

[damccorm]

LGTM

[mosche]

Thanks @damccorm