Commercial fridges already have this. They have a wedge under the hinge with a little shallow notch at the end. The weight of the door pushes the hinge on the wedge and it slowly closes the door when you’re not actively holding it open. The notch is so that it will hold open and is paired with a kick plate so you can give a little boot as you’re walking away to get it back on its closing game.

Look at public restroom stall doors for an example of what I’m talking about.