Ensure LDAPS with verify_certificates enabled can rely on Omnibus trusted_certs

Follow up on https://gitlab.com/gitlab-org/gitlab-ce/issues/33662, comment https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13915#note_38909601

Ensure LDAPS with verify_certificates enabled can rely on Omnibus trusted_certs as described in https://docs.gitlab.com/omnibus/settings/ssl.html.

If it works as expected, that will prevent some support requests when verify_certificates is enabled by default in 10.0.

If it does not work as expected, we should try to see if we can make it work.

• Assuming this works, open an MR to note in the LDAP docs and note in the LDAP configs (in CE and Omnibus) that you could just add your cert this way