Add DataSource parameter for artifacts endpoints

[sciapanCA]

No description provided.

[gemini-code-assist]

Code Review

This pull request introduces support for an optional --data-source parameter in the fetch.py and relationships.py scripts, as well as the underlying API client, to disambiguate identifiers that exist in multiple data sources. It also updates the documentation and CLI output to surface data source names and IDs. The review feedback identifies several edge cases in CLI argument parsing where providing --data-source at the end of a command without a value is not handled correctly, and points out an inconsistency in grep.py when handling dataSource as a string instead of a dictionary.

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