sysutils/slurm-wlm: Improve rc.d scripts

• Add rc.conf knobs for slurm_conf, logdir, rundir, pidfile and logfile paths
• Run slurmctld and slurmd under daemon(8) in foreground mode (-D)
• Implement status/reload using pidfiles and procname via rc.subr helpers
• Create log/run directories with appropriate ownership and permissions
• Ensure clean shutdown and avoid stray helper processes across restarts
• Preserve compatibility with existing *_flags and SLURM_CONF settings

PR: 290211