Fixed the broken beam python on flink with PortableRunner

[liferoad]

Tested this locally by building the beam-flink-runner container image and running the simple test.

Created flink-conf/flink-conf.yaml and the yaml file contains:

parallelism.default: 23
taskmanager.memory.network.fraction: 0.2
taskmanager.memory.network.max: 2gb

Then started the container:

docker run --net=host -v /path/flink-conf:/flink-conf beam-flink-runner

Simple test:

import apache_beam as beam

from apache_beam.options.pipeline_options import PipelineOptions

options = PipelineOptions([
    "--runner=PortableRunner",
    "--job_endpoint=localhost:8099",
    "--environment_type=LOOPBACK"
])

with beam.Pipeline(options=options) as pipeline:
  elements = pipeline | beam.Create([1, 2, 3, 4, 5])

  # Use Map to apply a function to each element
  elements | 'Print elements' >> beam.Map(print)

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[liferoad]

Add a note here: no need to change the docker entrypoint. We can pass in --flink-conf-dir /flink-conf directly when calling docker run. See #33182