Make Redis URL configurable

app/models/setting.rb

@@ -2,6 +2,13 @@
 class Setting < RailsSettings::Base
   cache_prefix { "v1" }
 
+  #
+  # Internal services
+  #
+
+  field :redis_url, type: :string, readonly: true,
+    default: ENV["REDIS_URL"] || "redis://localhost:6379/0"
+
   #
   # Registrations
   #