Sending messages via Infobip supports only one number

[dsmoljanovic]

When sending SMS to Infobip provider only the first number receives it; others don't get anything. This line here shows that only first member is picked and others ignored https://github.com/messagebird/sachet/blob/6575a2433b2f3c028eb153dde4b7bf5b61a41f5b/provider/infobip/infobip.go#L40

Infobip API supports sending to multiple destinations. Also, perhaps shift to use newer API (https://www.infobip.com/docs/api#channels/sms/send-sms-message)