mount "data volumes" from "generic nodes defaults" on KFP components

[thesuperzapper]

Background

Currently, we support mounting data volume on "generic nodes" while in a Kubeflow Pipeline.
I think we should also mount these volumes to the "KFP component nodes".

This will allow data to be exchanged between "generic" and "KFP" components through the mounted volumes, (at least partially solving #1765), and would also facilitate data exchange between "KFP" components themselves.

Implementation

For "generic nodes" we currently pass volume_mounts to the ExecuteFileOp constructor, which are looped-over and added with self.add_volume().

(NOTE: self.add_volume() works on ExecuteFileOp because it extends from kfp.dsl.ContainerOp)

Similarly, we can add these volumes to the ContainerOps generated from KFP component definitions by looping over the list with add_volume().

Considerations

• We should rename the "Generic nodes defaults" to "Node Defaults" as they would no longer only be for generic nodes
  • (We may want to say in the description that "Data Volumes" are not applied to Airflow components)
• We should add node-specific configs for "Data Volume" mounts on KFP components (like we already do for generic ones)
• If we want, we can also apply the global "Environment Variables" using container.add_env_variable()

[ptitzler]

Good timing! This also came up in a recent discussion.

[ptitzler]

@lehrig, fyi