Add Apple Pay functionality

[dimaportenko]

you can use it as follows

BTClient.showApplePayViewController({
        merchantIdentifier: 'your.merchant.id',
        paymentSummaryItems: [
          {label: 'Subtotals', amount: subtotals},
          {label: 'Shipping', amount: shipping},
          {label: 'Totals', amount: totals},
        ]
      })
        .then((response) => {
          console.log(response);
          if (response.nonce) {

          }
        });