feat: convert gemini format to openai chat completions

relay/channel/vertex/adaptor.go

@@ -44,6 +44,10 @@ type Adaptor struct {
 	AccountCredentials Credentials
 }
 
+func (a *Adaptor) ConvertGeminiRequest(c *gin.Context, info *relaycommon.RelayInfo, request *dto.GeminiChatRequest) (any, error) {
+	return request, nil
+}
+
 func (a *Adaptor) ConvertClaudeRequest(c *gin.Context, info *relaycommon.RelayInfo, request *dto.ClaudeRequest) (any, error) {
 	if v, ok := claudeModelMap[info.UpstreamModelName]; ok {
 		c.Set("request_model", v)