Add examples for producing/consuming when ldap and oauth is enabled

In the example [ldap_to_oauth_plus_ldap](https://github.com/confluentinc/confluent-kubernetes-examples/tree/master/security/oauth/upgrade/ldap_to_oauth_plus_ldap) a Confluent cluster with OAuth and LDAP is deployed. It would be nice if the example could also show an example of producing or consuming with external listeners for both of these options.

**Scenario 1**: I want to produce to Kafka with my keycloak client using OAuth.
**Scenario 2**: I want to produce to Kafka using my LDAP user.

Start with the ldap_to_oauth_plus_ldap example under security/oauth/upgrade and trace how its external listeners and authentication configuration are demonstrated. Add example workflows showing production or consumption with a Keycloak OAuth client and with an LDAP user, covering both scenarios described in the issue.

Written by the indexing model from the issue text.