Wired up enableAutomaticTax feature flag to Stripe API

The automatic_tax option is required to enable tax collection for
Stripe Checkout sessions. We've used getters here rather than an
explicit function, might wanna change that in future.

ghost/core/core/server/services/stripe/config.js

@@ -1,5 +1,6 @@
 const logging = require('@tryghost/logging');
 const tpl = require('@tryghost/tpl');
+const labs = require('../../../shared/labs');
 
 const messages = {
     remoteWebhooksInDevelopment: 'Cannot use remote webhooks in development. See https://ghost.org/docs/webhooks/#stripe-webhooks for developing with Stripe.'
@@ -64,6 +65,9 @@ module.exports = {
             ...keys,
             ...urls,
             enablePromoCodes: config.get('enableStripePromoCodes'),
+            get enableAutomaticTax() {
+                return labs.isSet('stripeAutomaticTax');
+            },
             webhookSecret: webhookSecret,
             webhookHandlerUrl: webhookHandlerUrl.href
         };

ghost/stripe/lib/StripeAPI.js

@@ -20,6 +20,7 @@ const STRIPE_API_VERSION = '2020-08-27';
  * @prop {string} secretKey
  * @prop {string} publicKey
  * @prop {boolean} enablePromoCodes
+ * @prop {boolean} enableAutomaticTax
  * @prop {string} checkoutSessionSuccessUrl
  * @prop {string} checkoutSessionCancelUrl
  * @prop {string} checkoutSetupSessionSuccessUrl
@@ -395,6 +396,9 @@ module.exports = class StripeAPI {
             cancel_url: options.cancelUrl || this._config.checkoutSessionCancelUrl,
             // @ts-ignore - we need to update to latest stripe library to correctly use newer features
             allow_promotion_codes: discounts ? undefined : this._config.enablePromoCodes,
+            automatic_tax: {
+                enabled: this._config.enableAutomaticTax
+            },
             metadata,
             discounts,
             /*

ghost/stripe/lib/StripeService.js

@@ -73,6 +73,9 @@ module.exports = class StripeService {
             secretKey: config.secretKey,
             publicKey: config.publicKey,
             enablePromoCodes: config.enablePromoCodes,
+            get enableAutomaticTax() {
+                return config.enableAutomaticTax;
+            },
             checkoutSessionSuccessUrl: config.checkoutSessionSuccessUrl,
             checkoutSessionCancelUrl: config.checkoutSessionCancelUrl,
             checkoutSetupSessionSuccessUrl: config.checkoutSetupSessionSuccessUrl,