Implement the PaymentAuthorize, PaymentSync, Refund and RefundSync flows for Paystack

[jarnura]

Follow the steps outlined in the add_connector.md file.

Implement the PaymentAuthorize, PaymentSync, Refund, RefundSync, and Webhooks flows for Paystack connector.
Connector doc (Paystack): https://paystack.com/docs/payments/payment-channels/

• Payment Authorize:
  Authorize call to be made via Electronic Fund Transfer (payment method).
  Implement impl ConnectorIntegration<Authorize, PaymentsAuthorizeData, PaymentsResponseData> for Paystack to make Payment Authorize call.
• Payment Sync:
  Implement impl ConnectorIntegration<PSync, PaymentsSyncData, PaymentsResponseData> for Paystack in paystack.rs to make Payment Sync call.
• Refund:
  Implement impl ConnectorIntegration<Execute, RefundsData, RefundsResponseData> for Paystack in paystack.rs to make Refund call.
• RefundSync:
  Implement impl ConnectorIntegration<RSync, RefundsData, RefundsResponseData> for Paystack in paystack.rs to make Refund Sync call.
• Webhooks:
  There are two types of webhooks Payment, and Refund which to be implemented in impl webhooks::IncomingWebhook for Paystack in paystack.rs to receive the incoming webhooks sent by the connector.

Modify the get_headers() and get_url() according to the connector documentation.

Implement the Request and Response types and proper status mapping(Payment and Refund) in the transformers.rs file.

Webhooks - Paystack sends a webhook with payment and refund status, we have to catch those and update in the db as well.

Run the following commands before raising the PR -

cargo clippy
cargo +nightly fmt --all

Ref PR: #7286