It may very well sound weird, but you do not need any certificates to make LDAPS work. I had spent endless hours but the solution was a 1 liner.
Add the below line to /etc/openldap/ldap.conf (Might vary depending on distro)
Make sure you have the below entry to your pg_hba.conf.
i) If SSL is set to off or commented in ...
I have never done this, but my understanding is that the certs need to configured into your LDAP library configuration, not your PostgreSQL. So that would probably be configured in /etc/ldap/ldap.conf. Also, there would be no key. You are just verifying certs, not signing new ones.
Of the links in your comment, the 2nd is only describing using TLS for the ...