chore: Replace eventBus with mitt.js [CW-3275] (#9539)

# Replace the deprecated `eventBus` with mitt.js

## Description

Since eventBus and it's respective methods are deprecated and removed
from all future releases of vue, this was blocking us from migrating.
This PR replaces eventBus with
[mitt](https://github.com/developit/mitt). I have created a wrapper
mitt.js to simulate the same old event names so it's backwards
compatible, without making a lot of changes.


Fixes # (issue)

## Type of change

Please delete options that are not relevant.

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality not to work as expected)
- [ ] This change requires a documentation update

## How Has This Been Tested?

1. Made sure all the places we're listening to bus events are working as
expected.
2. Respective specsf or the events from mitt.


## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented on my code, particularly in hard-to-understand
areas
- [x] 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
- [x] Any dependent changes have been merged and published in downstream
modules

app/javascript/dashboard/store/utils/api.js

@@ -9,6 +9,7 @@ import {
 } from '../../helper/scriptHelpers';
 import { LOCAL_STORAGE_KEYS } from 'dashboard/constants/localStorage';
 import { LocalStorage } from 'shared/helpers/localStorage';
+import { emitter } from 'shared/helpers/mitt';
 
 Cookies.defaults = { sameSite: 'Lax' };
 
@@ -18,8 +19,8 @@ export const setLoadingStatus = (state, status) => {
 };
 
 export const setUser = user => {
-  window.bus.$emit(CHATWOOT_SET_USER, { user });
-  window.bus.$emit(ANALYTICS_IDENTITY, { user });
+  emitter.emit(CHATWOOT_SET_USER, { user });
+  emitter.emit(ANALYTICS_IDENTITY, { user });
 };
 
 export const getHeaderExpiry = response =>
@@ -70,8 +71,8 @@ export const deleteIndexedDBOnLogout = async () => {
 };
 
 export const clearCookiesOnLogout = () => {
-  window.bus.$emit(CHATWOOT_RESET);
-  window.bus.$emit(ANALYTICS_RESET);
+  emitter.emit(CHATWOOT_RESET);
+  emitter.emit(ANALYTICS_RESET);
   clearBrowserSessionCookies();
   clearLocalStorageOnLogout();
   const globalConfig = window.globalConfig || {};