fix(cli): fix collaborator role handling in dataset metadata update

[sridipbasu]

Summary

kaggle datasets metadata --update crashes whenever dataset-metadata.json
contains collaborators. The CLI was passing the collaborator role directly as
a string (for example, "writer"), while the SDK expects a
CollaboratorType enum. This caused a TypeError before the request was sent.

Fix

Convert collaborator role strings to the corresponding
CollaboratorType enum using the existing lookup_enum() helper, keeping the
behavior consistent with other enum fields already handled by the CLI.

Tests

Added tests to verify that:

• collaborator role strings are converted correctly
• multiple collaborators are handled correctly
• invalid collaborator roles raise an appropriate error

Ran:

pytest tests/unit/test_dataset_metadata_update.py

[sridipbasu]

Attaching screenshots of the reproduction. The first shows the test dataset being created successfully and the metadata update command being run. The second shows the dataset-metadata.json used for reproduction. The CLI crashes locally with TypeError: role must be of type CollaboratorType before any request is sent to the API.

[stevemessick]

/gcbrun