Reimplement global attachement to be more efficient

[meiertgrootes]

The current implementation of gloabla attachement erases edge data and is inefficient i its use of exisiting DGL built-ins. @vmgaribay has implemted functionality which could be used for a much more efficient imolementation in random_edge_noise.
It would be desirable to reimplement on the basis thereof.

[vmgaribay]

maybe the functionality of 'local_attachment_homophily' is a bit closer to 'global_attachment' now that I think on it