"listener.name.clients" typo is in the documentation

Issue

• "listener.name.clients" typo is in the documentation. It should be "listener.name.client", not "listener.name.clients".

• "listener.name.clients"(typo) are used in two places(1)(2).

• This causes a login error in OAuthBearerLoginModule because OAuthBearerUnsecuredLoginCallbackHandler is used, instead of the JaasCleiantOauthLoginCallbackHandler provided by Strimzi.

• (1) 4.10.2.2. OAuth 2.0 authentication configuration in the Kafka cluster
  https://access.redhat.com/documentation/en-us/red_hat_amq/7.6/html-single/using_amq_streams_on_rhel/index#con-oauth-authentication-broker-str

• (2) 4.10.5.2. Configuring OAuth 2.0 support for Kafka brokers
  https://access.redhat.com/documentation/en-us/red_hat_amq/7.6/html-single/using_amq_streams_on_rhel/index#con-oauth-strimzi-config-str