Update deprecated subscriber implementation

[a11rew]

Issue

The subscriber implementation pattern used in the plugin's automatic order capturing subscriber has been deprecated since Medusa v1.18.

This warning is logged out when a server with the plugin is started as a result

The subscriber in /app/node_modules/medusa-payment-paystack/dist/subscribers/orderCapturer.js is missing a config.

Expected outcome

At the completion of this issue the automatic order capturing subscriber would have been updated to use the new Subscriber API. This guide describes the new API and migration details.