Add flags in vm.upgrade for scheduling

[mdechiaro]

Is your feature request related to a problem? Please describe.
There is an option to schedule a VM hardware upgrade, so it upgrades when the system is rebooted. It would be a useful feature to have in govc, especially when you need to automate the upgrade of VMs so that they upgrade themselves during a scheduled patch cycle.

Describe the solution you'd like
govc vm.upgrade -vm $VM -scheduled -policy < always | never | onSoftPowerOff >

Describe alternatives you've considered
Currently the VM needs to be powered off, upgraded, then powered on. It's more efficient, especially when dealing with many VMs, to schedule this during a patch cycle and reboot.

Additional context
API docs I can find about it:

https://vdc-download.vmware.com/vmwb-repository/dcr-public/b50dcbbf-051d-4204-a3e7-e1b618c1e384/538cf2ec-b34f-4bae-a332-3820ef9e7773/vim.vm.ScheduledHardwareUpgradeInfo.HardwareUpgradeStatus.html

https://vdc-download.vmware.com/vmwb-repository/dcr-public/b50dcbbf-051d-4204-a3e7-e1b618c1e384/538cf2ec-b34f-4bae-a332-3820ef9e7773/vim.vm.ScheduledHardwareUpgradeInfo.html

https://vdc-download.vmware.com/vmwb-repository/dcr-public/b50dcbbf-051d-4204-a3e7-e1b618c1e384/538cf2ec-b34f-4bae-a332-3820ef9e7773/vim.vm.ScheduledHardwareUpgradeInfo.HardwareUpgradePolicy.html

[github-actions]

Howdy 🖐   mdechiaro ! Thank you for your interest in this project. We value your feedback and will respond soon.

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[dougm]

Hi @mdechiaro , just catching up here I see some commits in your fork referencing this issue.. do you want to open a PR against the govmomi repo so we can review and merge your changes?

[mdechiaro]

@dougm Thanks for the reminder about this. I had to re-prioritize my workload last month and then took a long vacation. I plan revisiting this within the next two weeks and will submit a PR.