respect fronted-logging.enabled flag (#29107)

public/app/app.ts

@@ -206,6 +206,7 @@ export class GrafanaApp {
     });
 
     registerEchoBackend(new PerformanceBackend({}));
+    if (config.sentry.enabled) {
       registerEchoBackend(
         new SentryEchoBackend({
           ...config.sentry,
@@ -213,6 +214,7 @@ export class GrafanaApp {
           buildInfo: config.buildInfo,
         })
       );
+    }
 
     window.addEventListener('DOMContentLoaded', () => {
       reportPerformance('dcl', Math.round(performance.now()));