feat: messages extension (#4028)

* feat: private messages

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

@@ -0,0 +1,13 @@
+@php
+    /** @var \Flarum\Messages\Notification\MessageReceivedBlueprint $blueprint */
+@endphp
+
+@extends('flarum.forum::email.plain.notification.base')
+
+@section('content')
+{!! $translator->trans('flarum-messages.email.message_received.plain.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]),
+'{content}' => $blueprint->message->content
+]) !!}
+@endsection