Add perl dependency to SSL troubleshooting steps

When adding certificates in /etc/gitlab/trusted-certs, the recipe calls c_rehash in /opt/gitlab/embedded/bin, which requires a perl interpreter to run. Since gitlab-omnibus does not include perl and some OSs, such as CentOS Minimal, do not include it the certificates never get installed because c_rehash does not create the appropriate symlinks in /etc/gitlab/trusted-certs.

This MR adds a troubleshooting step to test for that, as well as a note that perl is needed for symlinks to be created.