media/sticker: fix lottie mime type

It's always gunzipped, so should never send the application/x-tgsticker mime.
Also, video/lottie+json was recently registered with IANA, so use that instead
of the old image/lottie+json: <https://www.iana.org/assignments/media-types/video/lottie+json>

pkg/connector/capabilities.go

@@ -116,7 +116,7 @@ var fileCaps = event.FileFeatureMap{
 		MimeTypes: map[string]event.CapabilitySupportLevel{
 			"image/webp": event.CapLevelFullySupported,
 			// TODO
-			//"image/lottie+json": event.CapLevelFullySupported,
+			//"video/lottie+json": event.CapLevelFullySupported,
 			//"video/webm": event.CapLevelFullySupported,
 		},
 	},

pkg/connector/media/sticker.go

@@ -54,17 +54,17 @@ type ConvertedSticker struct {
 func (c AnimatedStickerConfig) convert(ctx context.Context, data []byte) ConvertedSticker {
 	input := bytes.NewBuffer(data)
 	if c.Target == "disable" {
-		return ConvertedSticker{DataWriter: input, MIMEType: "application/x-tgsticker"}
+		return ConvertedSticker{DataWriter: input, MIMEType: "video/lottie+json"}
 	}
 
 	log := zerolog.Ctx(ctx).With().Str("animated_sticker_target", c.Target).Logger()
 
 	if !lottie.Supported() {
 		log.Warn().Msg("lottie not supported, cannot convert animated stickers")
-		return ConvertedSticker{DataWriter: input, MIMEType: "application/x-tgsticker"}
+		return ConvertedSticker{DataWriter: input, MIMEType: "video/lottie+json"}
 	} else if (c.Target == "webp" || c.Target == "webm") && !ffmpeg.Supported() {
 		log.Warn().Msg("ffmpeg not supported, cannot convert animated stickers")
-		return ConvertedSticker{DataWriter: input, MIMEType: "application/x-tgsticker"}
+		return ConvertedSticker{DataWriter: input, MIMEType: "video/lottie+json"}
 	}
 
 	dataWriter := new(bytes.Buffer)
@@ -102,7 +102,7 @@ func (c AnimatedStickerConfig) convert(ctx context.Context, data []byte) Convert
 			Msg("failed to convert animated sticker to target format")
 
 		// Fallback to original data
-		return ConvertedSticker{DataWriter: input, MIMEType: "application/x-tgsticker"}
+		return ConvertedSticker{DataWriter: input, MIMEType: "video/lottie+json"}
 	}
 
 	return ConvertedSticker{