Added support for licenses

[BrettPowell]

This adds an optional parameter for licenses to be added to dataproc images.

This parameter supports the gcloud syntax for passing in licenses of a list of licenses separates by commas inside of a string, with an optional space.

[medb]

May you explain what is use case for the extra licenses or even overriding licenses?

[functicons]

+1, this requires a product decision, we need to understand the use case first. In my opinion, we might not want customers to apply other licenses other than the default Dataproc license.

[BrettPowell]

To clarify I’m not asking for anything in GCP to change. We just want the ability to add to the list of licenses through this script. This behavior does not effect applied licenses from the original image.

The functionality of adding licenses to an image is something we already do in an additional automation step after building the Dataproc image.

The use case: We utilize licenses as a way to validate that our image is the base image for all our customer's images.