Automate App Store screenshot and metadata

[teolemon]

What

• [x] #11
• [ ] #12
• [ ] #13
• [ ] #14
• [ ] #15
• [ ] #16
• [ ] #17

Part of

• openfoodfacts/smooth-app#536

[monsieurtanuki]

For the record, about the iOS screenshots, the simulators I chose for my own app:

• 6.5" - iPhone 11 Pro Max (1242x2688)
• 5.5" - iPhone 8 Plus (1242x2208)
• ipad Pro (12.9") (4th generation) (2048x2732)