feat: Add sendTransactionMail method

[xiCO2k]

Hey,

I'm have the need to send a transactional mail from my system and looks like there is no method for that.

Right now I'm using this:

    /**
     * @param  array<string, string>  $replacements
     */
    public function sendTransactionMail(string $name, string $from, string $to, array $replacements): void
    {
        $this->post('transactional-mails/send', [
            'mail_name' => $name,
            'from' => $from,
            'to' => $to,
            'replacements' => $replacements,
        ]);
    }

But looks like we should have a method on sdk for that.

Thanks. ❤️

[Nielsvanpach]

Released in 1.3.0