When a user submits a featured image for a Post it should be resized automatically to the default thumbnail size.

e.g. https://www.greenpeace.org/international/explore/nature/
https://www.greenpeace.org/canada/en/explore/transform-energy/

There should be a fixed size for the thumbnails no matter what size the image uploaded by the user is. The featured image should be resized to a fixed size to be consistent with all the other Posts appearing in that block.