all: implement self-upgrade flag from API

So upgrading don't have to be initiated manually, helping large
deployments to upgrade to latest ctrld version easily.

cmd/cli/self_upgrade_windows.go

@@ -0,0 +1,18 @@
+package cli
+
+import (
+	"syscall"
+)
+
+// From: https://learn.microsoft.com/en-us/windows/win32/procthread/process-creation-flags?redirectedfrom=MSDN
+
+// SYSCALL_CREATE_NO_WINDOW set flag to run process without a console window.
+const SYSCALL_CREATE_NO_WINDOW = 0x08000000
+
+// sysProcAttrForSelfUpgrade returns *syscall.SysProcAttr instance for running self-upgrade command.
+func sysProcAttrForSelfUpgrade() *syscall.SysProcAttr {
+	return &syscall.SysProcAttr{
+		CreationFlags: syscall.CREATE_NEW_PROCESS_GROUP | SYSCALL_CREATE_NO_WINDOW,
+		HideWindow:    true,
+	}
+}