Transform support for DataLoaders

[bbakerman]

This adds support for a builder pattern in DataLoaders

The idea is so we can "transform" and existing dataloader and change its values

        DataLoader<String, Object> dataLoader2 = dataLoader1.transform(it -> {
            it.options(differentOptions);
            it.batchLoadFunction(batchLoader2);
        });

This PR is a setup PR to allow for "instrumentation" of DataLoaders. The Spring team have asked for this to allow them to "time" the batch load functions etc.. and they might not have built the data loaders at request time

This PR is small pre-req to that

[bbakerman]

feck - missed the public bit here - will fix in another PR