Decribe support for SVG and Lottie formats in image events

[MurzNN]

Suggestion
In most of current Matrix clients we can send as image only jpg, gif and webp file formats. But in the Spec it's not described the list of suitable formats for m.image events.
So now we are missing support for SVG and Lottie formats in Matrix clients.

This issue is vote to describe list of common image formats, that should be supported in clients, and include SVG and Lottie formats to the list of supported.

[MurzNN]

It's even a common case to place SVG logo (eg company logo) as Space/Room avatar, but Matrix clients don't allow this :(

[soloturn]

please consider and and how to handle telegrams compressed lottie (tgs), as well as the future dotLottie.

[soloturn]

security is a topic, see lottie vs lottie light on airbnb, and some hints for SVG on securitum.

there are approaches to increase security, e.g. WebMTD: Defeating Cross-Site Scripting Attacks Using Moving Target Defense.