Allow a user to disable peer check when using TLS/STARTTLS

This is useful when developing and on Docker setups. Despite setting
encryption to null, if a server supports STARTTLS with a self-signed
certificate, the mailer try to upgrade the connection with STARTTLS.

app/Config/mail.php

@@ -32,6 +32,7 @@ return [
             'encryption' => env('MAIL_ENCRYPTION', 'tls'),
             'username' => env('MAIL_USERNAME'),
             'password' => env('MAIL_PASSWORD'),
+            'verify_peer' => env('MAIL_VERIFY_PEER', true),
             'timeout' => null,
             'local_domain' => env('MAIL_EHLO_DOMAIN'),
         ],