Correct service-management docs/comments: this SDP fork is systemd/systemctl-managed, not init-based
- gen_sudoers.sh / opt_perforce_sdp_backup.sh / install_sdp.sh: fix FORK NOTE
comments that wrongly claimed the fork is init-based and would not use
systemctl. The .service units wrap the generated *_init scripts and the
perforce user controls p4d via systemctl (gen_sudoers generates exactly those
P4_SVC systemctl grants).
- SDP_PORT_SCOPE.md: reframe the init-vs-systemd note -- only upstream's
systemd-enforcement blocks are excluded; the fork uses systemd units that wrap
the still-callable init scripts.
- doc/SDP_Guide.Unix.md: make systemd/systemctl the primary documented
service-control path; demote chkconfig/SysV to a legacy note.
- doc/operational_scripts.md (new): full per-script catalog of the 22 fork-added
/p4/common/bin operational scripts.
- doc/maintenance_scripts.md: cross-link the new operational catalog.