Add optional S3 config/backend for ActiveStorage

config/environments/production.rb

@@ -110,9 +110,11 @@ Rails.application.configure do
   # Set this to true and configure the email server for immediate delivery to raise delivery errors.
   config.action_mailer.raise_delivery_errors = true
 
-  # TODO make configurable
-  # Store attachments in S3-compatible back-end
-  config.active_storage.service = :local
+  if ENV["S3_ENABLED"]
+    config.active_storage.service = :s3
+  else
+    config.active_storage.service = :local
+  end
 
   # Enable locale fallbacks for I18n (makes lookups for any locale fall back to
   # the I18n.default_locale when a translation cannot be found).