Don't render matomo tag manager on no url

1. If the config url is not set, we don't want to render the tag manager.
2. So, lets just add a check and return null. This could be the case that
    an env variable isn't set or that the env variable is set to empty.

frontend/templates/troubleshooting/components/TagManager.tsx

@@ -53,6 +53,10 @@ function MatomoScript() {
       }
    })();
 
+   if (!configUrl) {
+      return null;
+   }
+
    const scriptTag = `
         var c = "${configUrl}";