If it becomes necessary to manually install a plugin that is not bundled with the SonarQube image, or an updated version of an existing pluging is required, after downloading the plugin's JAR file execute the following command to copy it to the pod's plugin directory:
oc cp ./my-sonar-plugin.jar my-openshift-namespace/sonarqube-pod-name:/opt/sonarqube/extensions/plugins
A restart of the pod will be required after copying a new/updated plugin.