[WIP] Support dynamic allocation

[WeichenXu123]

Support dynamic allocation, in this PR:

    n_jobs is None will request 1 worker.
    n_jobs=-1 means requesting all available workers,
    but if cluster in dynamic allocation mode and available workers is zero
    then use spark_default_parallelism and trigger spark worker dynamic allocation

[Vincent-Maladiere]

Hey @WeichenXu123, I used your PR, and it works like a charm! This should be merged :)