read()ing protected Attributes should support user-supplied copying methods

Cloning a configuration attribute sometimes is not enough. For example when dealing with collections and immutable types we need to overcome the following:

Caused by: java.lang.UnsupportedOperationException
at org.infinispan.commons.util.Immutables$ImmutableTypedProperties.put(Immutables.java:622)
at org.infinispan.configuration.cache.IndexingConfigurationBuilder.setProperty(IndexingConfigurationBuilder.java:130)
at org.infinispan.configuration.cache.IndexingConfigurationBuilder.addProperty(IndexingConfigurationBuilder.java:107)