WILDFLY_OVERRIDING_ENV_VARS is not set on the EAP 8 runtime image

As mentioned in https://github.com/wildfly/wildfly-proposals/blob/main/management/WFCORE-5489_override_attribute_value_from_env_var.adoc, we decided to set the WILDFLY_OVERRIDING_ENV_VARS env var on the runtime image so that the ability to override management attribute values with env vars was enabled by default on OpenShift.

To do so, the WILDFLY_OVERRIDING_ENV_VARS env var must be set on the runtime image that is used as the base image when building the application image.