Verify coverage of producer data protection

[alexgarel]

Only moderators should be able to modify data protected by producers.

Verify it's the case via API and via webapp.

Verify it's advertised directly in the form so that user get right feedback for why he can't edit.

[github-actions]

This issue is stale because it has been open 90 days with no activity.

[stephanegigandet]

Current issues with protection of data from producers:

• There's a bug in the web form processing that disables the protection.
• In the API, there is a very broad protection of most fields and nutrients (if some data was sent by the producer, then all data is protected)
• In the web, nutrition is not protected.
• Images selected by producers are not protected, users can select another image.
• Packaging data is not protected.

[manon-corneille]

I tested this, and found that I could edit:

• Quantity
• Packaging data
• Ingredient and Nutrition photos

I couldn't edit:

• Nutrition table
• Front photos