Programatically create flows for publishing to flow registry

[malthe]

This is somewhat related to #5, but a continuation such that you create the desired flow programatically, optionally test it, and then publish it as a new version in the flow registry:

flow.publish("My bucket", "My flow name", "Flow description")

In a CI/CD pipeline integration, a new version would then get published only if there are changes to the most recent version.

Perhaps this is already possible, but in that case it would be great to have it showcased as an example in the documentation.