feat: support users to customize download ua

component/http/http.go

@@ -10,14 +10,12 @@ import (
 	"time"
 
 	"github.com/Dreamacro/clash/component/tls"
+	C "github.com/Dreamacro/clash/constant"
 	"github.com/Dreamacro/clash/listener/inner"
 )
 
-const (
-	UA = "clash.meta"
-)
-
 func HttpRequest(ctx context.Context, url, method string, header map[string][]string, body io.Reader) (*http.Response, error) {
+	UA := C.UA
 	method = strings.ToUpper(method)
 	urlRes, err := URL.Parse(url)
 	if err != nil {