Add Dataflow Apache Beam Java streaming system test

[olegkachur-e]

• add system test
• update docs
• add sources to the build jar file

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[potiuk]

Rebased but some init.py files should be added (pre-commit will do it automatically).

[olegkachur-e]

Rebased but some init.py files should be added (pre-commit will do it automatically).

@potiuk Thank you for the rebase!

I thought it's not quite correct to add init.py files into the Java sources, is there any way to exclude some resources folder from this check or another approach?

[potiuk]

I thought it's not quite correct to add init.py files into the Java sources, is there any way to exclude some resources folder from this check or another approach?

Sure - look at the sources of check-providers-subpackages-init-file-exist -> they are all configured in .pre-commit.yml and the script run here is scripts/ci/pre_commit/check_providers_subpackages_all_have_init.py -> and yes there are some exclusions there, you can likely figure out how to add yours.