Add support for non-preemptible secondary workers in Dataproc operator

[medb]

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[boring-cyborg]

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[turbaszek]

@medb thanks for your contribution! The ClusterGenerator is here only to preserver backward-compatibility. Currently, the DataprocCreateCluster operator accepts a dictionary that describes the cluster. In this way, we can easily cover all Dataproc cluster configurations without tones of additional code. So I would suggest to use the backports:
https://github.com/apache/airflow/tree/master/airflow/providers/google#installation

[medb]

Thank you for clarification, in this case I will close this PR because it's already possible to use DataprocCreateCluster operator to specify secondary workers preemptibility.