Allow declaring custom or multiple notification classes in health.php

[christosku]

BUG: When trying to create a custom notification for laravel-health I found out that RunHealthChecksCommand getFailedNotificationClass() returns a hardcoded Spatie\Health\Notifications\CheckFailedNotification::class which makes it impossible to override with your own notification.

• Make getFailedNotificationClass() return the first key (class name) from config('health.notifications.notifications')

This change should not have any effect in existing installations but would allow users to use their own notification by declaring it inside health.php:

'notifications' => [
    App\Notifications\CustomCheckFailedNotification::class => ['mail','teams','signal','irc'],
],

@freekmurze I went through the documentation and code and couldn't find another way to do this, other than creating a custom command, but that seemed like an overkill and maybe this could help others who need custom notifications.

[freekmurze]

Multiple notification classes seem overkill to me. Could you refactor this so there can be only one notification class?

[christosku]

Done!

[freekmurze]

Thanks!