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/modules/contact/components/AddCustomAttribute.vue

@@ -21,7 +21,7 @@
         :label="$t('CUSTOM_ATTRIBUTES.FORM.VALUE.LABEL')"
         :placeholder="$t('CUSTOM_ATTRIBUTES.FORM.VALUE.PLACEHOLDER')"
       />
-      <div class="flex justify-end items-center py-2 px-0 gap-2">
+      <div class="flex items-center justify-end gap-2 px-0 py-2">
         <woot-button
           :is-disabled="$v.attributeName.$invalid || isCreating"
           :is-loading="isCreating"
@@ -38,14 +38,12 @@
 
 <script>
 import Modal from 'dashboard/components/Modal.vue';
-import alertMixin from 'shared/mixins/alertMixin';
 import { required, minLength } from 'vuelidate/lib/validators';
 
 export default {
   components: {
     Modal,
   },
-  mixins: [alertMixin],
   props: {
     show: {
       type: Boolean,