This MR adds new application setting to network section
`allow_local_requests_from_system_hooks`. Prior to this change
system hooks were allowed to do local network requests by default
and we are adding an ability for admins to control it.
Gitlab::CurrentSettings will create ApplicationSetting.current if not
present which means we don't have to use `&.`. We can also more easily
use stub_application_setting in specs
GitLab Bot