[BUG] RAFT build broken by RMM change from thrust::optional to std::optional

[harrism]

Describe the bug
RAFT build is currently broken, see e.g.
https://github.com/rapidsai/devcontainers/actions/runs/8055346951/job/22001993724#step:7:13863

This is caused by the just-merged rapidsai/rmm#1464. I was under the impression that RAPIDS repos had been searched for usage of thrust::optional with the resource types that were changed in that PR, but RAFT slipped through the cracks due to a level of indirection (I assume).

The fix is to update https://github.com/rapidsai/raft/blob/branch-24.04/cpp/include/raft/core/device_resources_manager.hpp#L115-L123 to use std::optional.

I'm working on it.

[harrism]

Fixed by #2199