Kubernetes Components Should Ignore Empty Prefix Properties

Following recent changes on the main branch to support optional prefix properties for Kubernetes Leases and ConfigMaps, testing indicated that the Leader Election Manager and State Provider included empty strings as valid values. This changes the default behavior based on the default nifi.properties and state-management.xml including empty strings for prefix values. The components should be modified to ignore empty strings in addition to null values, aligning with current behavior prior to the introduction of these properties.