Allow setting key in mail config (#51618)

Like other mailer configuration which allows setting the key inside the configuration.

This is useful for when you have multiple mailers from the same transport, but for different accounts.

src/Illuminate/Mail/MailManager.php

@@ -303,7 +303,7 @@ protected function addSesCredentials(array $config)
     protected function createResendTransport(array $config)
     {
         return new ResendTransport(
-            Resend::client($this->app['config']->get('services.resend.key')),
+            Resend::client($config['key'] ?? $this->app['config']->get('services.resend.key')),
         );
     }