ai-proxy: support custom openai provider (#1176)

Co-authored-by: Kent Dong <ch3cho@qq.com>

plugins/wasm-go/extensions/ai-proxy/provider/baichuan.go

@@ -1,6 +1,7 @@
 package provider
 
 import (
+	"errors"
 	"fmt"
 
 	"github.com/alibaba/higress/plugins/wasm-go/extensions/ai-proxy/util"
@@ -20,6 +21,9 @@ type baichuanProviderInitializer struct {
 }
 
 func (m *baichuanProviderInitializer) ValidateConfig(config ProviderConfig) error {
+	if config.apiTokens == nil || len(config.apiTokens) == 0 {
+		return errors.New("no apiToken found in provider config")
+	}
 	return nil
 }