fix(api): derive host from storefront domain

Every storefront, including nested subdomains, uses its matching api.<hostname> endpoint.

src/environments/environment.ts

@@ -5,7 +5,7 @@ export const environment = {
   useMockBootstrapOnLocal: true,
   fallbackTenantKey: 'default',
   localhostApiUrl: '/api',
-  tenantApiTemplate: '{origin}/backend',
+  tenantApiTemplate: '{protocol}//api.{hostname}',
   tenantApiBaseUrls: {},
   brandName: 'Marketplace',
   brandFullName: 'Marketplace',