feat: add Baidu V2 channel support and improve model handling

relay/adaptor/baiduv2/main.go

@@ -0,0 +1,17 @@
+package baiduv2
+
+import (
+	"fmt"
+
+	"github.com/songquanpeng/one-api/relay/meta"
+	"github.com/songquanpeng/one-api/relay/relaymode"
+)
+
+func GetRequestURL(meta *meta.Meta) (string, error) {
+	switch meta.Mode {
+	case relaymode.ChatCompletions:
+		return fmt.Sprintf("%s/v2/chat/completions", meta.BaseURL), nil
+	default:
+	}
+	return "", fmt.Errorf("unsupported relay mode %d for baidu v2", meta.Mode)
+}