Generate also a webp file for images

[Mte90]

Requested Feature: the user attach an image but it will be helpful for performance that a webp image is generated for that image and that there is a redirect for those images if the browser support them.

Do you want to contribute this yourself as a pull request? (don’t worry about it if you don’t want to/can’t — someone else can take care of it)

• Yes, I have already written code for it (link if available and feasible)
• Yes, I don’t have code ready yet (that’s okay!)
• No (that’s okay too!)

Does this feature affect backwards compatibility? If yes, in what way?

Rationale and full description: it is a common standard to generate also a webp and provide to the users to speed up the download.