FEATURE: Give option to repurchase products multiple times (#46)

Feature requested here: https://meta.discourse.org/t/subscriptions-allow-users-to-purchase-one-time-products-multiple-times/173732/

There may be cases where a site admin wants to allow the repurchasing of a product. This implements the functionality by adding a repurchaseable toggle in the admin screen when creating a product. This saves an attribute to the Stripe product metadata.

When a user has already purchased an item with this toggle enabled, they will be able to purchase it again when browsing to `/s`.

app/controllers/discourse_subscriptions/admin/products_controller.rb

@@ -93,7 +93,10 @@ module DiscourseSubscriptions
           name: params[:name],
           active: params[:active],
           statement_descriptor: params[:statement_descriptor],
-          metadata: { description: params.dig(:metadata, :description) }
+          metadata: {
+            description: params.dig(:metadata, :description),
+            repurchaseable: params.dig(:metadata, :repurchaseable)
+          }
         }
       end
     end

app/controllers/discourse_subscriptions/subscribe_controller.rb

@@ -136,7 +136,8 @@ module DiscourseSubscriptions
         id: product[:id],
         name: product[:name],
         description: PrettyText.cook(product[:metadata][:description]),
-        subscribed: current_user_products.include?(product[:id])
+        subscribed: current_user_products.include?(product[:id]),
+        repurchaseable: product[:metadata][:repurchaseable]
       }
     end