That would be the architect and/or developer and would be part of the strata scheme submission for planning approval. It may be changed later, for instance when an owner or owners want to add a fence that wasn’t there to begin with and which is (or should be) installed as part of the by-law giving approval for the installation of the fence.
In that case the owners corp should insist that the fence is lot property to be maintained by the owners on either side, or one owner if they want it more than the other person does.