[#379] Fixing the bug where scanned products will show 200 as CO2e

[saurabhchatterjee23]

✅ I have read the contributing file

Summary

https://github.com/NMF-earth/nmf-app/issues/379

This bug happened if the slider was not moved before adding the scanned product to the emission lists. This happened because in the default value that was passed to the packageScanScreen the emission value that is read from Open Food database was not taken in consideration

Changelog

• Made changes to ProductScanned.tsx to set product scanned quantity instead of the total emission value
• Made changes to AddEmissionScreen to set the emission value after multiplying the quantity with the productCarbonFootprint that is fetched from the Open Food database

Demo

• Tested the App by scanning a product and not moving the slider and adding it to the emission list
• Tested the App by scanning a product and changing the quantity
• Tested the App by adding a custom product

[PierreBresson]

Works well ✅ Thanks @saurabhchatterjee23