Migrate integration tests away from `bitnamilegacy/openldap`

Bitnami was taken over by Broadcom/VMWare/Tanzu and decided to only provide paid, security hardened images. Therefore the existing images have been moved to a legacy repository where they will not receive updates anymore.

- [How to prepare for the Bitnami Changes coming soon](https://community.broadcom.com/blogs/beltran-rueda-borrego/2025/08/18/how-to-prepare-for-the-bitnami-changes-coming-soon)
- https://github.com/bitnami/containers/issues/83267

It is best to migrate to another image repository for the integration tests:
https://github.com/influxdata/telegraf/blob/4054043bf6005ca5dfef76e8a10df9385eee7e3a/plugins/inputs/ldap/ldap_test.go#L97
https://github.com/influxdata/telegraf/blob/4054043bf6005ca5dfef76e8a10df9385eee7e3a/plugins/inputs/openldap/openldap_test.go#L65

Start with plugins/inputs/ldap/ldap_test.go around line 97 and plugins/inputs/openldap/openldap_test.go around line 65, where the integration-test image references are linked. Identify the replacement image source and update both tests so they no longer use bitnamilegacy/openldap. Run the affected LDAP and OpenLDAP integration tests to verify they still pass.

Written by the indexing model from the issue text.