Enable Support for webp Stickers in iOS Element App and Automate Thumbnail Conversion to GIF#51

Unfortunately, the current iOS Element app does not support webp stickers. After testing, I have successfully enabled animated stickers in the iOS Element app. Below is an example sticker format: ```JSON { "body": "🔫", "url": "mxc://<my-home-server>/bmNWFYcyvThrPsgAHsMaFJBL", "info": { "w": 512, "h": 512, "size": 82887, "mimetype": "image/gif", "thumbnail_url": "mxc://<my-home-server>/bmNWFYcyvThrPsgAHsMaFJBL", "thumbnail_info": { "w": 128, "h": 128, "size": 2580, "mimetype": "image/gif" } }, "msgtype": "m.sticker", "id": "mxc://<my-home-server>/bmNWFYcyvThrPsgAHsMaFJBL", "net.maunium.telegram.sticker": null }, ``` During testing, I found that both the sticker and its thumbnail must have the mimetype set to image/gif. However, since the uploaded thumbnail is in webp format, I've utilized the sticker URL as the thumbnail URL, which has proven to work flawlessly. I'm now considering if there's a more automated approach to this issue, such as converting the thumbnail into a GIF format and uploading it to the Synapse Matrix server. Any insights on this matter would be greatly appreciated.