Allow the upload of WebM animations

[Victor]

Which part of the project should be enhanced?

https://github.com/hedgedoc/hedgedoc/blob/develop/backend/src/media/media.service.ts#L51-L64

Is your enhancement request related to a problem? Please describe.

Currently, Hedgedoc allows uploading GIF format, but WebM files are not supported. While formally one is animation and the other is a video, sites like https://imgur.com/ have used WEBM successfully for a long time, browsers support it, and GIF has larger file sizes with lower quality. Thus, allowing WEBM uploads should fix that.

Describe the solution you'd like

• Let the users upload WebM files
• Let the users configure HedgeDoc to ignore the file size limits if the part DerMolly mentions is a concern at this stage of the implementation: I'm using it locally, and the files are mine
• Ideally, fix the parser so that ![](WEBM_URL) turns into <video autoplay draggable="false" playsinline="" loop="" preload="auto" src="WEBM_URL" width="100%"></video>

Describe alternatives you've considered

HedgeDoc either supports WebM well, or it doesn't. The alternative is to leave GIF as a default and it leads to worse quality, file size and FPS in an animation.

Additional context

No response