feat: challenge 54 pipe obs signal (#903)

apps/signal/54-pipe-observable-to-signal/src/app/currency.pipe.ts

@@ -0,0 +1,15 @@
+import { inject, Pipe, PipeTransform } from '@angular/core';
+import { map, Observable } from 'rxjs';
+import { CurrencyService } from './currency.service';
+
+@Pipe({
+  name: 'currency',
+  standalone: true,
+})
+export class CurrencyPipe implements PipeTransform {
+  currencyService = inject(CurrencyService);
+
+  transform(price: number): Observable<string> {
+    return this.currencyService.symbol$.pipe(map((s) => `${price}${s}`));
+  }
+}