Add featured image functionality

[DavidLemayian]

Description

For each item (project/organisation), they could benefit quite a bit with a featured image that would be used in the header of the item page or as a thumbnail in the card. This would then translate well for Open Graph.

Screenshots

[WIP]:
We'd include mockups here. Please share them in comments and we'll update here with selected one.

Files

N/A (for now)

Tasks

• Create mockups of what this would look like.
• Add Featured Image column to Working gSheet.
• Write code to save image to s3.
• Write code to create version with overlay of AfricanCOMMONS logo for social sharing.
• Update project page to display featured image.