Implement the Folksonomy Engine API (custom properties for products, will be useful for Open Products Facts) in the Swift SDK

[teolemon]

What

• Implement the Folksonomy Engine API (custom properties for products, will be useful for Open Products Facts)
• https://api.folksonomy.openfoodfacts.org/docs

Part of

• 🎯 What can I work on ? (openfoodfacts-swift) #1