v2.28.0-05-05-2026: fix: add RPM prefetch for Konflux hermetic builds of MPI images

Konflux hermetic builds inject cachi2 which disables remote dnf repos,
causing openssh-server and RDMA package installs to fail. Add rpms.in.yaml
and repo configs for RPM prefetching via cachi2.

CUDA: only openssh-server needed (RDMA packages already in base image).
ROCm: openssh-server, rdma-core, infiniband-diags needed. Lock file must
be generated on an entitled RHEL system.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>