增加对于gemini-exp-1114模型的支持，映射到v1beta

feat(gemini): add support for gemini-exp-1114 model

- Add gemini-exp-1114 to ModelList in constant.go
- Update GetRequestURL in adaptor.go to use v1beta API version for gemini-exp-1114
- Keep backward compatibility for other models

This change enables the use of the experimental gemini-exp-1114 model by correctly routing its requests to the v1beta API endpoint while maintaining existing functionality for other models.

relay/channel/gemini/adaptor.go

@@ -30,13 +30,22 @@ func (a *Adaptor) Init(info *relaycommon.RelayInfo) {
 }
 
 func (a *Adaptor) GetRequestURL(info *relaycommon.RelayInfo) (string, error) {
-	// 从映射中获取模型名称对应的版本，如果找不到就使用 info.ApiVersion 或默认的版本 "v1"
-	version, beta := constant.GeminiModelMap[info.UpstreamModelName]
-	if !beta {
-		if info.ApiVersion != "" {
-			version = info.ApiVersion
-		} else {
-			version = "v1"
+	var version string
+	
+	// 为特定模型指定版本
+	switch info.UpstreamModelName {
+	case "gemini-exp-1114":
+		version = "v1beta"
+	default:
+		// 从映射中获取模型名称对应的版本，如果找不到就使用 info.ApiVersion 或默认的版本 "v1"
+		var beta bool
+		version, beta = constant.GeminiModelMap[info.UpstreamModelName]
+		if !beta {
+			if info.ApiVersion != "" {
+				version = info.ApiVersion
+			} else {
+				version = "v1"
+			}
 		}
 	}