cp-solr-xml Init Container Does Not Set readOnlyRootFilesystem: true

The **cp-solr-xml** init container currently does not configure `readOnlyRootFilesystem: true`. However, this container does not appear to require a writable root filesystem for its functionality.

As a result, the container is not adhering to **Kubernetes** security best practices, which recommend setting `readOnlyRootFilesystem: true` for containers that do not need write access to their root filesystem. This helps to reduce the attack surface and improve overall security by preventing potential unauthorized write operations.

No file or test is named; search the operator's manifests or templates for the cp-solr-xml init container and inspect how its configuration is rendered. Update the container configuration so readOnlyRootFilesystem is true, then run the relevant Kubernetes rendering or integration tests. Done means the generated configuration includes the setting and existing tests pass.

Written by the indexing model from the issue text.