Optimize images by IMGBot

There is a pull request to optimize images.

Instead of merging it, would you install IMGBot Github app?
IMGBot is free for OSS. See https://imgbot.net/

I think only Python administrators can install the App.

If we do end up installing it, we need to add ImgBotApp to the list of CLA_TRUSTED_USERS for the-knights-who-say-ni.