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/components/widgets/LabelSelector.vue

@@ -33,7 +33,7 @@
 import AddLabel from 'shared/components/ui/dropdown/AddLabel.vue';
 import keyboardEventListenerMixins from 'shared/mixins/keyboardEventListenerMixins';
 import LabelDropdown from 'shared/components/ui/label/LabelDropdown.vue';
-import adminMixin from 'dashboard/mixins/isAdmin';
+import { useAdmin } from 'dashboard/composables/useAdmin';
 
 export default {
   components: {
@@ -41,7 +41,7 @@ export default {
     LabelDropdown,
   },
 
-  mixins: [adminMixin, keyboardEventListenerMixins],
+  mixins: [keyboardEventListenerMixins],
 
   props: {
     allLabels: {
@@ -54,6 +54,13 @@ export default {
     },
   },
 
+  setup() {
+    const { isAdmin } = useAdmin();
+    return {
+      isAdmin,
+    };
+  },
+
   data() {
     return {
       showSearchDropdownLabel: false,