(diagnostics/systemhealth) add some definitions

src/opnsense/scripts/systemhealth/definitions/gateway-quality.xml

+<?xml version="1.0"?>
+<systemhealth>
+    <file-match>.*-quality$</file-match>
+    <title>System Information - Quality </title>
+    <y-axis_label>seconds/%</y-axis_label>
+</systemhealth>

src/opnsense/scripts/systemhealth/definitions/interface-traffic.xml

+<?xml version="1.0"?>
+<systemhealth>
+    <file-match>.*-traffic$</file-match>
+    <title>System Information - Traffic </title>
+    <y-axis_label>Bits/Second</y-axis_label>
+</systemhealth>

src/opnsense/scripts/systemhealth/definitions/interface-vpnusers.xml

+<?xml version="1.0"?>
+<systemhealth>
+    <file-match>.*-vpnusers$</file-match>
+    <title>System Information - VPN Users </title>
+    <y-axis_label>users</y-axis_label>
+</systemhealth>