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/packs/application.js

@@ -15,6 +15,8 @@ import WootUiKit from '../dashboard/components';
 import App from '../dashboard/App';
 import i18n from '../dashboard/i18n';
 import createAxios from '../dashboard/helper/APIHelper';
+import { emitter } from '../shared/helpers/mitt';
+
 import commonHelpers, { isJSONValid } from '../dashboard/helper/commons';
 import router, { initalizeRouter } from '../dashboard/routes';
 import store from '../dashboard/store';
@@ -93,7 +95,8 @@ commonHelpers();
 
 window.WootConstants = constants;
 window.axios = createAxios(axios);
-window.bus = new Vue();
+Vue.prototype.$emitter = emitter;
+
 initializeChatwootEvents();
 initializeAnalyticsEvents();
 initalizeRouter();