Add vSAN data migration support for host.maintenance.enter

[darksoul42]

Is your feature request related to a problem? Please describe.
I currently have to use the GUI to put a host in maintenance mode on my vSAN clusters,
because in some cases I need to do a full data migration.

Describe the solution you'd like
Add an option to the "host.maintenance.enter" command:
-migrate-data [full|accessibility|none]

(Default : accessibility, which is already what govc ends up doing)

Describe alternatives you've considered
Alternative involves doing it manually via the vCenter GUI.

Currently, the default behavior is "ensure accessibility",
which is fine for most scenarios (upgrades/reboots),
just not the one where prolonged/permanent loss of the host might be expected.

Additional context
This would follow the options available as described here:
https://docs.vmware.com/en/VMware-vSphere/6.7/com.vmware.vsphere.virtualsan.doc/GUID-521EA4BC-E411-47D4-899A-5E0264469866.html

[github-actions]

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[github-actions]

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[dougm]

Pointers to related existing code for context:
govc host.maintenance commands: https://github.com/vmware/govmomi/tree/main/govc/host/maintenance
govc vsan commands: https://github.com/vmware/govmomi/blob/main/govc/vsan