In order for set readOnlyRootFilesystem=true, according to
https://github.com/arkmq-org/activemq-artemis-operator/discussions/1014

spec.deploymentPlan.containerSecurityContext + extraVolumeMounts

However, the extraVolumeMounts are not applied to initContainers.

This leads to two problems:
1. initcontainer can't be configured to readOnlyRootFilesystem=true
2. a semi workaround is to set the broker container readOnlyRootFilesystem=true by using

   spec:
      resourceTemplates:
        - selector:
            kind: "StatefulSet"
          patch:
            kind: "StatefulSet"
            spec:
              template:
                spec:
                  containers:
                    - name: "broker-container"
                      securityContext: 
                        readOnlyRootFilesystem: true