[LDAP] Allow to use Nextclouds trusted certificate store for LDAPS

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Is your feature request related to a problem? Please describe.
Currently, the LDAP module relies on certificates to be added to the system certificate store in /etc/ssl/certs in order to trust them. However especially in container deployments, it is not always possible to add custom certificates in there and rather hacky in the container world.

Describe the solution you'd like
It would be great if the LDAP module could additionally also trust the certificates that are added to the Nextcloud certificate store via occ security:certificates:import.

Describe alternatives you've considered
Maybe allow to configure LDAP_OPT_X_TLS_* in order to load the certificates from a different but writeable place?

Additional context
Currently, in AIO there are some workarounds but they are rather hacky.
Also see https://www.php.net/manual/en/ldap.constants.php#constant.ldap-opt-x-tls-cacertdir for the documentation for the ldap module.

cc @nextcloud/ldap

Start in the LDAP module and trace how LDAPS currently uses the system certificate store at /etc/ssl/certs, then compare that with certificates imported through occ security:certificates:import. Done means LDAPS can trust certificates from Nextcloud's certificate store without requiring installation in the system store, including container deployments.