[FEA] Add raft to rapids-compose

[seunghwak]

cuGraph and cuML are dependent on raft (https://github.com/rapidsai/raft), and can raft to be added to rapids-compose?

[trxcllnt]

Yes, definitely @seunghwak! Does it need to be added as a project for development, or is it a system or conda dependency?

[seunghwak]

There are people working on updating raft (including myself), so I think this needs to be a project.

[trxcllnt]

In this branch https://github.com/trxcllnt/rapids-compose/tree/add/raft/ until rapidsai/raft#13 is merged.