Klaviyo V2 Integration

The most recent version of this plugin is still using the old Klaviyo V1 API format. My clients are getting notified by Klaviyo that we need to update from V1 to V2.

Specifically, the function is ‘klaviyo_callback’ within \trackship-for-woocommerce\includes\integration\class-klaviyo-integration.php. Using /track is the V1 endpoint. It needs to be changed to the new endpoints detailed here: https://developers.klaviyo.com/en/reference/create_client_event