[Feature Request]: Update PythonMap transform to accept extra packages

[chamikaramj]

What would you like to happen?

This will allow executing PythonMap [1] x-lang transform with functions that require external dependencies.

[1] https://github.com/apache/beam/blob/master/sdks/java/extensions/python/src/main/java/org/apache/beam/sdk/extensions/python/transforms/PythonMap.java

Issue Priority

Priority: 2 (default / most feature requests should be filed as P2)

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