fix: gemini support webp file

relay/channel/gemini/relay-gemini.go

@@ -23,6 +23,7 @@ import (
 	"github.com/gin-gonic/gin"
 )
 
+// https://cloud.google.com/vertex-ai/generative-ai/docs/model-reference/inference?hl=zh-cn#blob
 var geminiSupportedMimeTypes = map[string]bool{
 	"application/pdf": true,
 	"audio/mpeg":      true,
@@ -30,6 +31,7 @@ var geminiSupportedMimeTypes = map[string]bool{
 	"audio/wav":       true,
 	"image/png":       true,
 	"image/jpeg":      true,
+	"image/webp":      true,
 	"text/plain":      true,
 	"video/mov":       true,
 	"video/mpeg":      true,