Set required proto fields in artifact messages

[eleftherias]

Summary

Set the fields in artifact messages as required or optional, to generate a correct OpenAPI spec.

Ref #4952

Fixes #(related issue)

Change Type

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• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

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Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[coveralls]

coverage: 54.771%. remained the same
when pulling c0aa515 on eleftherias:openapi-artifact-required-fields
into 135cf2f on mindersec:main.