feat: messages extension (#4028)

* feat: private messages

extensions/messages/views/emails/html/messageReceived.blade.php

@@ -0,0 +1,16 @@
+@php
+/** @var \Flarum\Messages\Notification\MessageReceivedBlueprint $blueprint */
+@endphp
+
+@extends('flarum.forum::email.html.notification.base')
+
+@section('notificationContent')
+{!! $formatter->convert($translator->trans('flarum-messages.email.message_received.html.body', [
+'{user_display_name}' => $blueprint->message->user->display_name,
+'{url}' => $url->to('forum')->route('messages.dialog', ['id' => $blueprint->message->dialog_id, 'near' => $blueprint->message->id])
+])) !!}
+@endsection
+
+@section('contentPreview')
+    {!! $blueprint->message->formatContent() !!}
+@endsection