feat(instructeurs import): display submit button only if file uploaded

app/javascript/controllers/enable_submit_if_uploaded_controller.tsx

@@ -0,0 +1,21 @@
+import { Controller } from '@hotwired/stimulus';
+import { enable, disable } from '@utils';
+
+export class EnableSubmitIfUploadedController extends Controller {
+  connect() {
+    const fileInput = document.querySelector(
+      'input[type="file"]'
+    ) as HTMLInputElement;
+    const submitButton = document.getElementById(
+      'submit-button'
+    ) as HTMLButtonElement;
+
+    fileInput.addEventListener('change', function () {
+      if (fileInput.files && fileInput.files.length > 0) {
+        enable(submitButton);
+      } else {
+        disable(submitButton);
+      }
+    });
+  }
+}