Add application settings cache timeout config

Default value of application_settings_timeout to 60

app/models/concerns/cacheable_attributes.rb

@@ -83,6 +83,6 @@ module CacheableAttributes
   end
 
   def cache!
-    self.class.cache_backend.write(self.class.cache_key, self, expires_in: 1.minute)
+    self.class.cache_backend.write(self.class.cache_key, self, expires_in: Gitlab.config.gitlab['application_settings_cache_seconds'] || 60)
   end
 end

config/gitlab.yml.example

@@ -165,6 +165,9 @@ production: &base
     ## Disable jQuery and CSS animations
     # disable_animations: true
 
+    ## Application settings cache expiry in seconds (default: 60)
+    # application_settings_cache_seconds: 60
+
   ## Reply by email
   # Allow users to comment on issues and merge requests by replying to notification emails.
   # For documentation on how to set this up, see http://doc.gitlab.com/ce/administration/reply_by_email.html