Add video previews and image thumbnails for examples

[aglitchman]

Information through graphics is understood much better than pure text.

It would be great if it were technically possible to design the examples directory with pictures and automatically playing videos if they are in the browser viewport:

• https://developer.playcanvas.com/tutorials/
• https://phaser.io/examples/v3.85.0/actions

Something like:

PS I am ready to make videos and pictures for all examples!