[Task]: Improve the example for PythonExternalTransform

[liferoad]

What needs to happen?

https://github.com/apache/beam/tree/master/sdks/python/apache_beam/examples/inference/multi_language_inference works with Beam 2.46.0 but

• it is broken with Beam 2.60.0 due to the new Python package changes (huggingface hub complains).
• Also the way to setup the maven project for this example does not work well. https://github.com/liferoad/beam-multi_language_inference is a working example with the generated pom file.
• To support ML, it will be better to show how to use custom container to avoid staging too many Python packages

Issue Priority

Priority: 2 (default / most normal work should be filed as P2)

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