[Python] Support large pipeline options via file (Fixes #37370)

[Mathdee]

Issue:
As described in #37370, running pipelines with large options on Dataflow causes fork/exec /usr/local/bin/python: argument list too long.
This occurs because the bootloader passes the complete JSON config via PIPELINE_OPTIONS environment variable --> exceeds the OS ARG_MAX limit.

The Fix:
This change uses an identical pattern from the Go SDK (Issue #27839, Commit e31e885) to Python.

1. boot.go(file): Writing the pipeline options to a temp file (pipeline_options.json) and sets the PIPELINE_OPTIONS_FILE environment variable.
2. sdk_worker_main.py(file): This then checks for PIPELINE_OPTIONS_FILE and loads the configs from the disk if present.

Outcome:

• Fixes [Feature Request]: Support large pipeline options in Python SDK #37370
• Feature Parity with Java and Go SDK's for handling large pipeline options
• Verified with unit tests that ensured priority of file-based loading.

---

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[gemini-code-assist]

Summary of Changes

Hello @Mathdee, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a robust solution for handling large pipeline options in the Python SDK, which previously led to an 'argument list too long' error due to operating system limitations on environment variable size. By transitioning from direct environment variable passing to a file-based approach, where options are written to a temporary file and its path is referenced, the system can now accommodate extensive configurations without encountering runtime failures. This enhancement ensures greater stability and consistency across SDKs.

Highlights

• Addresses Argument List Too Long Error: This pull request resolves the fork/exec /usr/local/bin/python: argument list too long error that occurs when running Dataflow pipelines with excessively large pipeline options, by preventing the complete JSON config from being passed directly via the PIPELINE_OPTIONS environment variable.
• File-based Pipeline Options: Pipeline options are now written to a temporary file named pipeline_options.json by the Go bootloader. The path to this file is then passed to the Python SDK worker via the PIPELINE_OPTIONS_FILE environment variable.
• Python SDK Worker Adaptation: The Python SDK worker (sdk_worker_main.py) has been updated to check for the PIPELINE_OPTIONS_FILE environment variable and load the pipeline configuration from the specified file if present, ensuring compatibility with the new mechanism.
• Feature Parity: This change brings the Python SDK into feature parity with the Java and Go SDKs for handling large pipeline options, using an identical pattern previously implemented in the Go SDK.

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[Mathdee]

All linting and integration checks are passing. Ready for review

[github-actions]

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R: @claudevdm for label python.

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[claudevdm]

@shunping can you take a pass at this since you have more context?