Auto-enable allowDuplicates for Redistribute with ALO streaming mode

[celeste-zeng]

Extract streaming mode from pipeline options, make the resulting Redistribute transform allow duplicates if either the original Redistribute allows duplicates or streaming mode is At-Least-Once.

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[celeste-zeng]

R: @Naireen

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[Naireen]

Just need some testing, look here for some pointers:

beam/runners/google-cloud-dataflow-java/src/test/java/org/apache/beam/runners/dataflow/DataflowRunnerTest.java

Line 2601 in af43a3b

private void testStreamingWriteOverride(PipelineOptions options, int expectedNumShards) {

[Naireen]

LGTM

[celeste-zeng]

R: @johnjcasey, hi, would you mind helping merge this? Thanks!