Add .webp support

[killermoehre]

Problem Description

.webp images are not rendered inline, but only provided for download. As more and more memes are in .webp format nowadays, supporting it like .png and .gif is important.

Proposed Solution

Support .webp the same as .png and .gif.

Describe alternatives you've considered

Transform the image server-side after upload. But this would probably open some path to code injection.

[andersk]

What version of Zulip Server do you have? We added WebP support in Zulip Server 9.0 (zulip/zulip#30480).

[killermoehre]

We run Zulip Server 10.1 self-hosted.

[timabbott]

This issue is in the wrong repository, it belongs in zulip/zulip. But also we already support webp. I'm going to close this. Please stop by chat.zulip.org with a more detailed report and we can try to figure out why it's not working for your installation.