Feature: Add $connection to MAIL_PROCESS_BEFORE event

[glensc]

This allows to have workflow event to delete email:

    /**
     * Ignore emails from being processed
     */
    public function blockIncomingMail(GenericEvent $event): void
    {
        /** @var ImapMessage $mail */
        $mail = $event->getSubject();

        if (!in_array($mail->getSender(), self::BLOCK_SENDERS, true)) {
            return;
        }

        $event->stopPropagation();
        $this->debug('Stopped mail from {}', ['sender' => $mail->getSender()]);
        $dumper = new MailDumper(self::DUMP_PATH);
        $dumper->dump($mail);

        /** @var ImapConnection $connection */
        $connection = $event['connection'];
        $connection->deleteMessage($mail);
    }