Honour RAILS_LOG_TO_STDOUT in config/environments/production.rb

12-factor apps should log to STDOUT, so that the platform can capture
the logs in a standard way.

This is already the case for newly created applications:
rails/rails@e9b96f0

(software-o-o was created prior to this change).

With this change, Rails will still log by default to
log/production.log, but if the platform sets RAILS_LOG_TO_STDOUT, it
will be able to capture the logs.

In the same way, if the systemd .service file sets

```
Environment="RAILS_LOG_TO_STDOUT=1"
```

Then you will be able to control/see the logs with journalctl.

config/environments/production.rb

@@ -22,4 +22,9 @@
   # Rake tasks automatically ignore this option for performance.
   config.eager_load = true
 
+  if ENV["RAILS_LOG_TO_STDOUT"].present?
+    logger           = ActiveSupport::Logger.new(STDOUT)
+    logger.formatter = config.log_formatter
+    config.logger    = ActiveSupport::TaggedLogging.new(logger)
+  end
 end