Shared money input should respond to change in currency (#654)

* Add step method to currency

* Change amount placeholder and step, when currency select change

* Lint

* Add test with auth

* Extract request to specific service

app/javascript/controllers/money_field_controller.js

@@ -0,0 +1,20 @@
+import { Controller } from "@hotwired/stimulus";
+import { CurrenciesService } from "services/currencies_service";
+
+// Connects to data-controller="money-field"
+// when currency select change, update the input value with the correct placeholder and step
+export default class extends Controller {
+  static targets = ["amount", "currency"];
+
+  handleCurrencyChange() {
+    const selectedCurrency = event.target.value;
+    this.updateAmount(selectedCurrency);
+  }
+
+  updateAmount(currency) {
+    (new CurrenciesService).get(currency).then((data) => {
+      this.amountTarget.placeholder = data.placeholder;
+      this.amountTarget.step = data.step;
+    });
+  }
+}