Loader: make behaviour consistent with Beam Enrich

[simplylizz]

1. Different arg name for dataflow jobs: --job-name for enricher vs --jobName for the loader.
2. Enricher fails if a job name isn't specified, the loader generates it (I think the first is preferred since they use the same input/output resources and conflicts here may have an unpredictable effect; also job-name is unique within dataflow project and allows you to update your pipelines).
3. Enricher exits after launching a pipeline while the loader hangs and outputs some info into console.

I think it would be nice to have consistent behavior.