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/WootWriter/Editor.vue

@@ -89,7 +89,7 @@ import {
 import { CONVERSATION_EVENTS } from '../../../helper/AnalyticsHelper/events';
 import { checkFileSizeLimit } from 'shared/helpers/FileHelper';
 import { uploadFile } from 'dashboard/helper/uploadHelper';
-import alertMixin from 'shared/mixins/alertMixin';
+import { useAlert } from 'dashboard/composables';
 import {
   MESSAGE_EDITOR_MENU_OPTIONS,
   MESSAGE_EDITOR_IMAGE_RESIZES,
@@ -119,7 +119,7 @@ const createState = (
 export default {
   name: 'WootMessageEditor',
   components: { TagAgents, CannedResponse, VariableList },
-  mixins: [keyboardEventListenerMixins, uiSettingsMixin, alertMixin],
+  mixins: [keyboardEventListenerMixins, uiSettingsMixin],
   props: {
     value: { type: String, default: '' },
     editorId: { type: String, default: '' },
@@ -611,7 +611,7 @@ export default {
       if (checkFileSizeLimit(file, MAXIMUM_FILE_UPLOAD_SIZE)) {
         this.uploadImageToStorage(file);
       } else {
-        this.showAlert(
+        useAlert(
           this.$t(
             'PROFILE_SETTINGS.FORM.MESSAGE_SIGNATURE_SECTION.IMAGE_UPLOAD_SIZE_ERROR',
             {
@@ -629,13 +629,13 @@ export default {
         if (fileUrl) {
           this.onImageInsertInEditor(fileUrl);
         }
-        this.showAlert(
+        useAlert(
           this.$t(
             'PROFILE_SETTINGS.FORM.MESSAGE_SIGNATURE_SECTION.IMAGE_UPLOAD_SUCCESS'
           )
         );
       } catch (error) {
-        this.showAlert(
+        useAlert(
           this.$t(
             'PROFILE_SETTINGS.FORM.MESSAGE_SIGNATURE_SECTION.IMAGE_UPLOAD_ERROR'
           )