Add CheckMK plugins

Document the currently used monitoring plugins (ref. #12)
Add the patched QEMU plugin

tools/cmk-plugins/README.md

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+# CheckMK Plugins
+
+Monitoring plugins for Openfest 2023
+
+## Installation
+
+Built-in plugins are downloaded directly from the monitoring site ([Internal URL](http://monitoring.openfest.org/)).
+Custom plugins are downloaded from this repo.
+
+The files are installed to `/usr/lib/check_mk_agent/plugins` with execute permissions (ex. `755`).
+
+## Plugin List
+
+| Name         | Type                                            | Installed on | Notes                        |
+| ------------ | ----------------------------------------------- | ------------ | ---------------------------- |
+| qemu         | [Custom](https://exchange.checkmk.com/p/qemu-1) | sonata       | Patched to work on debian 12 |
+| smart        | Built-in                                        | sonata       | Disk SMART monitoring        |
+| isc_dhcpd.py | Built-in                                        | dns          | DHCP pool usage              |

tools/cmk-plugins/qemu

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+#!/bin/bash
+
+# based upon 'qemu' from
+# 12/2010 Matthias Henze
+# Lizenz: GPL v2
+#
+# updated for libvirtd (virsh) by
+# Jonathan Mills 09/2011
+#
+# updated by
+# Christian Burmeister 05/2015
+#
+# updated formating:
+# Bastian Kuhn 08/2018
+# 
+# Update PID regexp:
+# Albert Stefanov 10/2023
+
+if which virsh >/dev/null; then
+    echo '<<<qemu>>>'
+    virsh list | grep -v 'State' | grep -v '^--' | grep -v '^$' | while read L
+    do
+            ID=$(echo $L | awk '{print $1}')
+            NAME=$(echo $L | awk '{print $2}')
+            STATE=$(echo $L | awk '{print $3}')
+            MEM=$(virsh dominfo $NAME | grep 'Used memory' | awk '{print $3}')
+            let MEM=MEM/1024
+            PID=$(pgrep -f -- "/qemu-system-x86_64 .*-name guest=$NAME")
+            if [ -n "$PID" ]; then
+                    DATA=$(top -p $PID -n 1 -b | sed '${/^$/d}' | tail -1 | awk -- '{print $9" "$10}')
+            else
+                    DATA=""
+            fi
+            echo $ID" "$NAME" "$STATE" "$MEM" "$DATA
+    done
+fi
+