FeatureTransformer should allow the collection bounds not to be encoded as well

FeatureTransformer asks the collections it's encoding for bounds in order to generate the boundedBy FeatureCollection child.
That element is actually optional, and computing it might require very significant amount of time if the returned collection is big (think tables of millions of records, in particular with Oracle that does not have an efficient way to compute the table bounds).
So we should allow whoever is using the encoder to choose wheter that element is generated, or not.