Add option to disable/enable overprovisioning functionality of existing VMSS

[d-mankowski-synerise]

Related command
az vmss update

Is your feature request related to a problem? Please describe.
It is not possible to enable/disable overprovisioning via AZ CLI, once VMSS has been created

Describe the solution you'd like
To be able to enable/disable overprovisioning functionality of existing VMSS via CLI, e.g. az vmss update --enable-overprovision {true, false}

Describe alternatives you've considered
N/A

Additional context
It is possible to enable/disable overprovision via AZ CLI during VMSS creation only, via az vmss create --disable-overprovision

[yonzhan]

Thank you for opening this issue, we will look into it.