[Doc 7.3.0.Beta] changes to liveness/readiness probes when migrating to EAP 7.3 images

Same behaviour documented under JBEAP-17464 should be documented for all EAP 7.3 images. Behaviour changed for OCP 3 as well as OCP 4.

Original text:
This jira is follow up to JBEAP-16858.

There should be added new chapter Migration application to Openshift 4 to Getting Started with JBoss EAP for OpenShift Container Platform [1].

JBEAP-16858 changed behaviour of liveness and readiness probles on OCP 4. Context can be found in description of CLOUD-2742.

If liveness probe was configured like:

livenessProbe:
        exec:
          command:
            - /bin/bash
            - '-c'
            - /opt/eap/bin/livenessProbe.sh
        initialDelaySeconds: 0
        timeoutSeconds: 1
        periodSeconds: 10
        successThreshold: 1
        failureThreshold: 3

One call of {{ /opt/eap/bin/livenessProbe.sh}} took 5 sec on OCP 3 before it returned. On OCP 4 it took less than 1 sec.

So for example for configuration of liveness probe above the container inside pod would be restarted after ~35 sec but on OCP 4 after ~23 sec in case that probe will report that server is down. Configuration of the probes should be adjusted to reflect this change.

[1] https://access.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.2/html/getting_started_with_jboss_eap_for_openshift_container_platform/index