Add a conf_root for configuration data and use it

[alexgarel]

What

• Following folders are mixed in the data folder, and called in the code using root_data.

• ecoscore
• emb_codes
• forest-footprint
• ingredients
• lang
• packager-codes
• po
• taxonomies
• templates

• But they are not real application data, they are configuration data (they come with deployment and should not be modified locally).
• So they should have a different root.
• In the code it would be ideal to have a data_root and conf_root and use them appropriately.
• For the time being, in production data_root and conf_root could be the same path, whereas in preprod they would be separated (data_root is a volume, conf_root is in the image).

Part of

• Refactor Product Opener #5527

[alexgarel]

This should also resolve #6020 (comment)

[github-actions]

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