Add adaptive image generation feature

Could you guys add adaptive image generation to LSCache? I.e. the ability to generate and serve multple image sizes for different screen sizes to improve loading times. This is the only feature that third party services like Shortpixel offer which LSCache doesn't. There are plugins to do it but they process images in php which is expensive. Being able to do this at the server level in OLS would mean we can ditch external image optimisation services once and for all :)

There are a couple of plugins you could borrow code from:
https://wordpress.org/plugins/adaptive-images/
https://wordpress.org/plugins/shortpixel-adaptive-images/

Start by reviewing the LSCache and OpenLiteSpeed integration points, then compare the approaches used by the linked Adaptive Images and ShortPixel Adaptive Images plugins. Done would require a defined design for generating and serving multiple image sizes at the server level without relying on third-party services.

Written by the indexing model from the issue text.