Add OBG datasets

[yuehhua]

• [ ] nodeproppred
  • [x] ogbn-proteins
  • [x] ogbn-products
  • [x] ogbn-arxiv
  • [ ] ogbn-mag
  • [ ] ogbn-papers100M
• [ ] linkproppred
  • [x] ogbl-ppa
  • [x] ogbl-collab
  • [x] ogbl-citation2
  • [ ] ogbl-wikikg2
  • [x] ogbl-ddi
  • [ ] ogbl-biokg
• [ ] graphproppred
  • [ ] ogbg-molhiv
  • [ ] ogbg-molpcba
  • [ ] ogbg-ppa
  • [ ] ogbg-code2

Ref: OGB

[zsz00]

how is it going now?