[OpenShift Guide] Provide a guidance how to customize default DB connection validation checker if desired

Originally initiated by SSOSUP-100, within the RHSSO-2300 Jira we plan to add a definition of a default, generic DB connection validation checker for RH-SSO OpenShift templates, spawning also an accompanied DB pod (see RHSSO-2300 for reasoning / motivation / rationale, why this change is required).

The concept of DB connection validation checker (& how to configure it) is described e.g. in the following two articles:

• https://access.redhat.com/solutions/156103
• https://access.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.3/html/configuration_guide/datasource_management#configure_database_connection_validation_settings

The default DB connection validation checker definition will be set / implemented as part of RHSSO-2300. The point of this documentation Jira is to describe the procedure / steps, that need to be done in the case, the user would like to customize the used DB connection checker (for example change it from the default "org.jboss.jca.adapters.jdbc.extensions.novendor.JDBC4ValidConnectionChecker" one to Oracle specific "org.jboss.jca.adapters.jdbc.extensions.oracle.OracleValidConnectionChecker" in the case the customer would be using an Oracle JDBC driver).

The list of various configurable connection checkers is available here:

• https://access.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.3/html/configuration_guide/datasource_management#configure_database_connection_validation_settings (section _Choose one of the validation mechanisms. _)

Note: The necessary steps, needed to switch the used DB connection validation checker will be described / put together yet, as part of the work at RHSSO-2300 issue.