feat(oam): port LibreNMS agent tooling from KNELServerBuild [#474]

Port the live LibreNMS monitoring patterns from the legacy
KNELServerBuild repo into oam/librenms-agent/, joining the existing
OAM tooling (oxidized, unpoller, smokeping, netdisco):

- agent/ — upstream check_mk agent + snmp-extend scripts (dmi, dpkg,
  mysql, ntp-client, ntp-server, os-updates, postfix, raspberry, smart,
  ss, ups-nut), copied verbatim (md5-verified), never to be edited here
- setup.sh — deploy module ported from ProjectCode/Modules/OAM/
  oam-librenms.sh; only the legacy framework bootstrap was replaced
  with plain bash (path constants + print_info -> echo)
- snmp-sudo.conf — Debian snmpd sudo rule the extends require
  (Debian-snmp NOPASSWD /bin/cat); carried as a file only, sudoers
  install is a policy decision per AGENTS.md

Lint gates: extend the existing upstream-skip mechanism for the
verbatim agent scripts (tests/shellcheck.sh + check-rules.sh prune,
same precedent as archive/provisioning/Agents/librenms), and fix the
stale skip path there (provisioning/ moved to archive/provisioning in
6244c1c; the bash extends have been failing the whole-repo shellcheck
gate since).

💘 Generated with Crush

Assisted-by: Crush:glm-5.2

oam/librenms-agent/agent/os-updates.sh

@@ -0,0 +1,73 @@
+#!/usr/bin/env bash
+################################################################
+# copy this script to /etc/snmp/ and make it executable:       #
+# chmod +x /etc/snmp/os-updates.sh                             #
+# ------------------------------------------------------------ #
+# edit your snmpd.conf and include:                            #
+# extend osupdate /opt/os-updates.sh 			       #
+#--------------------------------------------------------------#
+# restart snmpd and activate the app for desired host          #
+#--------------------------------------------------------------#
+# please make sure you have the path/binaries below            #
+################################################################ 
+BIN_WC='/usr/bin/wc'
+BIN_GREP='/bin/grep'
+CMD_GREP='-c'
+CMD_WC='-l'
+BIN_ZYPPER='/usr/bin/zypper'
+CMD_ZYPPER='-q lu'
+BIN_YUM='/usr/bin/yum'
+CMD_YUM='-q check-update'
+BIN_DNF='/usr/bin/dnf'
+CMD_DNF='-q check-update'
+BIN_APT='/usr/bin/apt-get'
+CMD_APT='-qq -s upgrade'
+BIN_PACMAN='/usr/bin/pacman'
+CMD_PACMAN='-Sup'
+
+################################################################
+# Don't change anything unless you know what are you doing     #
+################################################################
+if [ -f $BIN_ZYPPER ]; then
+    # OpenSUSE
+    UPDATES=`$BIN_ZYPPER $CMD_ZYPPER | $BIN_WC $CMD_WC`
+    if [ $UPDATES -ge 2 ]; then
+        echo $(($UPDATES-2));
+    else
+        echo "0";
+    fi
+elif [ -f $BIN_DNF ]; then
+    # Fedora
+    UPDATES=`$BIN_DNF $CMD_DNF | $BIN_WC $CMD_WC`
+    if [ $UPDATES -ge 1 ]; then
+        echo $(($UPDATES-1));
+    else
+        echo "0";
+    fi
+elif [ -f $BIN_PACMAN ]; then
+    # Arch
+    UPDATES=`$BIN_PACMAN $CMD_PACMAN | $BIN_WC $CMD_WC`
+    if [ $UPDATES -ge 1 ]; then
+        echo $(($UPDATES-1));
+    else
+        echo "0";
+    fi
+elif [ -f $BIN_YUM ]; then
+    # CentOS / Redhat
+    UPDATES=`$BIN_YUM $CMD_YUM | $BIN_WC $CMD_WC`
+    if [ $UPDATES -ge 1 ]; then
+        echo $(($UPDATES-1));
+    else
+        echo "0";
+    fi
+elif [ -f $BIN_APT ]; then
+    # Debian / Devuan / Ubuntu
+    UPDATES=`$BIN_APT $CMD_APT | $BIN_GREP $CMD_GREP 'Inst'`
+    if [ $UPDATES -ge 1 ]; then
+        echo $UPDATES;
+    else
+        echo "0";
+    fi
+else
+    echo "0";
+fi