Fix name conflict with icinga2-common

Avoid name conflict with broken systemd checkcomand definition in
icinga2-common.

global-templates/commands.conf

@@ -104,6 +104,6 @@ object CheckCommand "pgsql_socket" {
   vars.pgsql_username = "nagios"
 }
 
-object CheckCommand "systemd" {
+object CheckCommand "custom_systemd" {
   command = [ PluginContribDir + "/check_systemd" ]
 }

global-templates/services.conf

@@ -153,7 +153,7 @@ apply Service "ssh" {
 apply Service "systemd" {
   import "generic-service"
 
-  check_command = "systemd"
+  check_command = "custom_systemd"
 
   assign where host.vars.debian_release && host.vars.debian_release >= 12
 }