Remove any stunnel reference and usage

[ppatierno]

Because of this PR strimzi/strimzi-kafka-operator#9840 on the upstream Strimzi project, we are removing the support for the Bidirectional Topic Operator so the corresponding TLS sidecar as well.
It means that stunnel is not needed anymore.
We should remove any reference and usage to stunnel within the Kafka images build for AMQ Streams.

[fvaleri]

This is done as part of #9840. Do you see some leftover?

[ppatierno]

Nope but there is a work to do in our cekit related files here. It's not related with upstream.

[k-wall]

Looking at the 2.8 branch, we've still got references to stunnel, including the installation on a additional RPM. This will give us a great potential for CVEs. All of these references are to be removed, right?

Should we raise a JIRA to make sure we get this done for 2.8?

grep -ir stunnel .
./kafka/kafka-3.7.0/image.yaml:    - stunnel
./kafka/kafka-3.6.0/image.yaml:    - stunnel
./kafka/modules/kafka/base/install.sh:mkdir $STUNNEL_HOME
./kafka/modules/kafka/base/install.sh:cp -r ${SCRIPTS_DIR}/stunnel/* ${STUNNEL_HOME}/
./kafka/modules/kafka/base/install.sh:chmod -R 755 ${STUNNEL_HOME}
./kafka/modules/kafka/base/module.yaml:  - name: "STUNNEL_HOME"
./kafka/modules/kafka/base/module.yaml:    value: "/opt/stunnel"