Add a CLI for Ludwig AutoML

[justinxzhao]

One idea, mirroring ludwig.automl.auto_train()

ludwig automl --dataset=<>
    --target=
    --enable_hyperopt= # whether to run hyperopt, default False.
    --time_limit_s= # How long to run hyperopt for. If specified, hyperopt is enabled.
    --tune_for_memory=
    --output_directory=
    --random_seed=
    --user_config=
    --use_reference_config=

One notable difference is that we'll want to set hyperopt to be disabled by default, which is consistent with other automl offerings like flaml.

[justinxzhao]

@anneholler FYI