added download certificate and key in zip format

server/Configure.go

@@ -9,6 +9,7 @@ func Configure() {
 	http.Handle("/", api.SpaHandler(http.FS(api.Frontend)))
 	http.HandleFunc("/api/certs", api.Certs)
 	http.HandleFunc("/api/certs/root", api.RootCert)
+	http.HandleFunc("/api/certs/download/", api.CertKeyDownloadZip)
 	http.HandleFunc("/api/certs/create", api.CreateCert)
 	http.HandleFunc("/api/certs/delete", api.DeleteCert)
 }