Support array params in Mailable header

[teodoriu]

Hi,

I recently had to use sendinblue as mailer.

To be able to send custom params the params should be sent in the header method but the current implementation doesn't support array parameters, only text.

It's ok to send a pull request with the modifications? I think there are 2 files that needs to be modified.

Edit: i just found that i can use "using" on Envelope

 using: [
                function (Email $message) {
                    $message->getHeaders()->addParameterizedHeader('params', 'params', [
                        'LINK' => 'link'
                    ]);
                },
            ]