feat: challenge 43 input signal

apps/angular/signal-input/src/main.ts

@@ -0,0 +1,7 @@
+import { bootstrapApplication } from '@angular/platform-browser';
+import { AppComponent } from './app/app.component';
+import { appConfig } from './app/app.config';
+
+bootstrapApplication(AppComponent, appConfig).catch((err) =>
+  console.error(err),
+);