feat: Replace contentTypeMixin within the component (#9802)

# Pull Request Template

## Description

This PR will completely remove the `contentTypeMixin` and be used in the
component as it is.

Fixes
https://linear.app/chatwoot/issue/CW-3465/rewrite-contenttypemixin-mixin-as-a-helper

## Type of change

- [x] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

Take a look at this component
`app/javascript/dashboard/components/widgets/conversation/Message.vue`


## 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

app/javascript/dashboard/components/widgets/conversation/Message.vue

@@ -158,7 +158,7 @@ import InstagramStory from './bubble/InstagramStory.vue';
 import InstagramStoryReply from './bubble/InstagramStoryReply.vue';
 import Spinner from 'shared/components/Spinner.vue';
 import alertMixin from 'shared/mixins/alertMixin';
-import contentTypeMixin from 'shared/mixins/contentTypeMixin';
+import { CONTENT_TYPES } from 'shared/constants/contentType';
 import { MESSAGE_TYPE, MESSAGE_STATUS } from 'shared/constants/messages';
 import { generateBotMessageContent } from './helpers/botMessageContentHelper';
 import { BUS_EVENTS } from 'shared/constants/busEvents';
@@ -184,7 +184,7 @@ export default {
     InstagramStoryReply,
     Spinner,
   },
-  mixins: [alertMixin, messageFormatterMixin, contentTypeMixin],
+  mixins: [alertMixin, messageFormatterMixin],
   props: {
     data: {
       type: Object,
@@ -482,6 +482,9 @@ export default {
       }
       return '';
     },
+    isEmailContentType() {
+      return this.contentType === CONTENT_TYPES.INCOMING_EMAIL;
+    },
   },
   watch: {
     data() {