[FEATURE REQUEST] implementing support for custom notification channels

[Carnicero90]

Kinda built-in support for custom notifications. Had to change viaQueues as well to make it compatible with this commit.
Sample Usage:
`<?php

class customFWChannel {
public function send($notifiable, \Akaunting\Firewall\Notifications\AttackDetected $a) {
\Log::debug('sending to a custom channel');
}
}

config()->set('firewall.notifications.custom', [
'enabled' => true,
'channel' => customFWChannel::class,
'queue' => 'customqueue'
]);

$fakeAttack = (object) [
"ip" => "192.168.240.1",
"level" => "medium",
"middleware" => "url",
"user_id" => 0,
"url" => "http:https://localhost/admin",
"referrer" => "NULL",
"request" => "",
"updated_at" => "2023-10-02T08:53:24.000000Z",
"created_at" => "2023-10-02T08:53:24.000000Z",
"id" => 61
];
(new \Akaunting\Firewall\Notifications\Notifiable)->notify(
new \Akaunting\Firewall\Notifications\AttackDetected($fakeAttack)
);`