Migrate charm from legacy interface pgsql to the modern postgresql_client

[Alex Lutay]

Hi,

It is a bugreport to request migration from the legacy interface pgsql to the modern postgresql_client:
https://github.com/canonical/charm-relation-interfaces/blob/main/interfaces/postgresql_client/v0/README.md

The legacy interface is still supported by modern charm but will be removed soon, in the scope of migration to Nobel/24.04. Therefor it is important to switch openldap-charmers-openlda charm from legacy to modern charm/track/interface.

JFYI, The legacy charm postgresql from latest/stable is deprecated and superseded by modern charm postgresql from 14/stable (read more here: https://charmhub.io/postgresql-k8s/docs/e-legacy-charm).

Thank you!