Make external sorter Hadoop free

Right now the Java sorter extension depends on Hadoop SequenceFile for external sort. It'll be nice to re-implement it without the dependency to avoid conflicts.

Pull request adds a new option to switch to native sorting, the default behavior remains Hadoop sorting.

    final BufferedExternalSorter.Options sorterOpts =
        BufferedExternalSorter
            .options()
            .withExternalSorterType(ExternalSorter.Options.SorterType.HADOOP);

...

        .apply(SortValues.create(sorterOpts));