FirecREST doesn't return num_mpiprocs

[khsrali]

slurm scheduler plugin parses two additional key values: num_mpiprocs & num_machines from Slurm's squeue response. The later is number of nodes in use, and the former is number of cpus.

FirecREST server however doesn't return the raw response of squeue to use, but parse it themselves and return a modified raw response, in which they don't specify num_mpiprocs.

However, I'm not aware of any crucial usecase in aiida-core for num_mpiprocs.
Therefore we just document here for future if needed as suggested by @agoscinski