feat: Replace alertMixin usage with useAlert (#9793)

# Pull Request Template

## Description

This PR will replace the usage of `alertMixin` from the code base with
the `useAlert` composable.

Fixes
https://linear.app/chatwoot/issue/CW-3462/replace-alertmixin-usage-with-usealert

## Type of change

- [x] Breaking change (fix or feature that would cause existing
functionality not to work as expected)

## How Has This Been Tested?

Please refer this issue description

https://linear.app/chatwoot/issue/CW-3462/replace-alertmixin-usage-with-usealert


## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

---------

Co-authored-by: Sojan Jose <sojan@pepalo.com>

app/javascript/dashboard/helper/pushHelper.js

@@ -1,7 +1,7 @@
 /* eslint-disable no-console */
 import NotificationSubscriptions from '../api/notificationSubscription';
 import auth from '../api/auth';
-import { emitter } from 'shared/helpers/mitt';
+import { useAlert } from 'dashboard/composables';
 
 export const verifyServiceWorkerExistence = (callback = () => {}) => {
   if (!('serviceWorker' in navigator)) {
@@ -69,19 +69,13 @@ export const registerSubscription = (onSuccess = () => {}) => {
       onSuccess();
     })
     .catch(() => {
-      emitter.emit(
-        'newToastMessage',
-        'This browser does not support desktop notification'
-      );
+      useAlert('This browser does not support desktop notification');
     });
 };
 
 export const requestPushPermissions = ({ onSuccess }) => {
   if (!('Notification' in window)) {
-    emitter.emit(
-      'newToastMessage',
-      'This browser does not support desktop notification'
-    );
+    useAlert('This browser does not support desktop notification');
   } else if (Notification.permission === 'granted') {
     registerSubscription(onSuccess);
   } else if (Notification.permission !== 'denied') {