Add "PRODUCT_PROMOS_ENABLED" environment variable

.env-dist

@@ -74,3 +74,4 @@ SUPPORTED_LOCALES="*"
 SENTRY_DSN=""
 
 BREACH_RESOLUTION_ENABLED=1
+PRODUCT_PROMOS_ENABLED=1

app-constants.js

@@ -41,6 +41,7 @@ const kEnvironmentVariables = [
   "HIBP_NOTIFY_TOKEN",
   "DATABASE_URL",
   "PAGE_TOKEN_TIMER",
+  "PRODUCT_PROMOS_ENABLED",
   "SENTRY_DSN",
   "SUPPORTED_LOCALES",
   "DELETE_UNVERIFIED_SUBSCRIBERS_TIMER",