fix(windows): register dd-procmgr-service as LocalSystem in Wix

Match process-agent and system-probe: the Wix service installer now uses
LocalSystem instead of ddagentuser. ServiceCustomAction already sets
LocalSystem at install time; this closes the initial-registration gap.

Author: jose-manuel-almaza

tools/windows/DatadogAgentInstaller/WixSetup/Datadog Agent/AgentInstaller.cs

@@ -692,8 +692,8 @@ private Dir CreateBinFolder()
                 Constants.ProcmgrServiceName,
                 "Datadog Process Manager",
                 "Manage Datadog agent processes",
-                "[DDAGENTUSER_PROCESSED_FQ_NAME]",
-                "[DDAGENTUSER_PROCESSED_PASSWORD]");
+                "LocalSystem",
+                null);
             agentBinDir.AddFile(new WixSharp.File(_agentBinaries.ProcmgrService, procmgrService));
             agentBinDir.Add(new EventSource
             {