Only use RequestStore for current_application_settings during a request
What does this MR do?
This fixes an issue where the RequestStore was being populated with the settings in the unicorn master during the rails initializers. Each forked worker would then start their first request with an uncleaned RequestStore.
This resulted in the unicorn master always holding on to the application_settings it started up with, regardless of changes made to the database. And the first request of each forked worker would start with those potentially outdated settings.