Silence rack-timeout INFO messages

These unstructured messages are quite noisy and don't provide much
useful information in production:

```
source=rack-timeout id=RhEremul7w2 timeout=60000ms service=5ms \
state=completed
source=rack-timeout id=VMaWDTdCQo1 timeout=60000ms state=ready
```

Relates to https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/9123

config/initializers/rack_timeout.rb

@@ -12,6 +12,8 @@
 if Gitlab::Runtime.puma? && !Rails.env.test?
   require 'rack/timeout/base'
 
+  Rack::Timeout::Logger.level = Logger::ERROR
+
   Gitlab::Application.configure do |config|
     config.middleware.insert_before(Rack::Runtime, Rack::Timeout,
                                     service_timeout: ENV.fetch('GITLAB_RAILS_RACK_TIMEOUT', 60).to_i,