feat(opnsense): enable PID file monitoring for Defguard Gateway service

Replace nocheck flag with proper PID file configuration to enable OPNsense
service status monitoring. The service now correctly tracks the gateway
process state via PID file.

Changes:
- Remove 'nocheck' flag from service definition
- Add dynamic PID file path reading from user configuration
- Set default PID file location to /var/run/defguard_gateway.pid
- Add default value to PidFile model field for consistency
- Update form to display default PID file location hint
- Simplify config.toml template to always output pidfile with default

The PID file location can now be customized by users through the UI, or
will default to /var/run/defguard_gateway.pid. This ensures OPNsense can
properly monitor and report the gateway service status.

Author: jamtur01

opnsense/src/etc/inc/plugins.inc.d/defguardgateway.inc

@@ -3,15 +3,17 @@ function defguardgateway_services()
 {
     $services = [];
 
+    $pidfile = (string) (new OPNsense\DefguardGateway\DefguardGateway())->general->PidFile;
+
     $services[] = [
         "description" => "Defguard Gateway",
         "configd" => [
             "start" => ["defguard_gateway start"],
             "restart" => ["defguard_gateway restart"],
             "stop" => ["defguard_gateway stop"],
         ],
+        "pidfile" => empty($pidfile) ? "/var/run/defguard_gateway.pid" : $pidfile,
         "name" => "defguard_gateway",
-        "nocheck" => true,
     ];
 
     return $services;

opnsense/src/opnsense/mvc/app/controllers/OPNsense/DefguardGateway/forms/general.xml

@@ -42,6 +42,7 @@
     <type>text</type>
     <hint>Save PID to this file.</hint>
     <help>Optional: write PID to this file.</help>
+    <hint>Default value: /var/run/defguard_gateway.pid</hint>
   </field>
   <field>
     <id>defguardgateway.general.SyslogSocket</id>

opnsense/src/opnsense/mvc/app/models/OPNsense/DefguardGateway/DefguardGateway.xml

@@ -30,6 +30,7 @@
         <Required>Y</Required>
       </UseSyslog>
       <PidFile type="TextField">
+        <default>/var/run/defguard_gateway.pid</default>
         <Required>N</Required>
       </PidFile>
       <SyslogSocket type="TextField">

opnsense/src/opnsense/service/templates/OPNsense/DefguardGateway/config.toml

@@ -20,9 +20,7 @@ stats_period = {{ OPNsense.defguardgateway.general.StatsPeriod|default(60) }}
 # Required: name of WireGuard interface
 ifname = "{{ OPNsense.defguardgateway.general.IfName|default("wg0") }}"
 # Optional: write PID to this file
-{% if not helpers.empty('OPNsense.defguardgateway.general.PidFile') %}
-pidfile = "{{ OPNsense.defguardgateway.general.PidFile }}"
-{% endif %}
+pidfile = "{{ OPNsense.defguardgateway.general.PidFile|default("/var/run/defguard_gateway.pid") }}"
 # Required: enable logging to syslog
 {% if OPNsense.defguardgateway.general.UseSyslog == "1" %}
 use_syslog = true