add open files ulimit option for gitaly
This is adding a new setting to /etc/gitlab/gitlab.rb to set a gitaly open files ulimit. By default, no limit will be set which leads to a limit of 50000 (inherited from the parent runit process).
Related to https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/7390, to enable us to alert if gitaly uses too many file descriptors.