Add toasts to UI (#25449)

Fixes https://github.com/go-gitea/gitea/issues/24353

In some case like async success/error, it is useful to show toasts in UI.

web_src/js/modules/toast.test.js

@@ -0,0 +1,17 @@
+import {test, expect} from 'vitest';
+import {showInfoToast, showErrorToast, showWarningToast} from './toast.js';
+
+test('showInfoToast', async () => {
+  await showInfoToast('success 😀', {duration: -1});
+  expect(document.querySelector('.toastify')).toBeTruthy();
+});
+
+test('showWarningToast', async () => {
+  await showWarningToast('warning 😐', {duration: -1});
+  expect(document.querySelector('.toastify')).toBeTruthy();
+});
+
+test('showErrorToast', async () => {
+  await showErrorToast('error 🙁', {duration: -1});
+  expect(document.querySelector('.toastify')).toBeTruthy();
+});