feat(windows): add recoverable existing-agent credential upgrade

agents/windows/MinerOpsAgentGUI.ps1

@@ -204,9 +204,11 @@ $testButton.Add_Click({
         }
 
         $hub = [string]$config.hub_url
+        $agentId = [string]$config.agent_id
         $secret = [string]$config.agent_secret
 
         $headers = @{
+            "X-MinerOps-Agent-ID" = $agentId
             "X-MinerOps-Agent-Secret" = $secret
         }