Fix Docker build error by adding fallback for python3.12-distutils

[utkarshparekh]

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The Ubuntu 20.04 base image with the deadsnakes/ppa does not provide the
python3.12-distutils package as a separate entity, causing the Docker build
to fail. This commit modifies the Dockerfile to:

• Exclude python3.12-distutils from the initial apt-get install command
  using grep.
• Install python3-distutils as a fallback, which provides distutils support
  for the default Python version.
• Add a conditional installation attempt for python3.12-distutils, suppressing
  errors and logging a message if unavailable.

This ensures build compatibility across environments where python3.12-distutils
may not be available. Tested successfully with the updated Dockerfile.

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[Abacn]

Thanks for suggesting the fixes. This Dockerfile has been out-of-date for a while. A preferable fix would be bump to ubuntu-24.04 than patch the Dockerfile

[Abacn]

instead of patch "grep -v python3.12-distutils" one can remove it in https://github.com/apache/beam/blob/master/dev-support/docker/pkglist directly

[utkarshparekh]

Thank you for the feedback, @Abacn! I agree that bumping the base image to a newer Ubuntu version (e.g., 24.04) is a more sustainable solution.

To ensure compatibility, I’ll test the updated Dockerfile by:

• Building the image locally with docker build.
• Running the Beam environment setup (./start-build-env.sh) to verify the fix.
• Executing the Java and Python wordCount examples (./gradlew :examples:java:wordCount and ./gradlew :sdks:python:wordCount) to check downstream impact.

I’ll submit an updated PR with these changes once testing is complete. Please let me know if you have a preferred Ubuntu version or additional tests to include!