[azure-cli] stop using `reservedInstanceCount` and use `preWarmedInstanceCount`

[anthonychu]

Azure/azure-cli#11752

SDK changes required have been released. This item is now unblocked.

[adiun]

@anthonychu I'm trying to figure out how to set this value in ARM template or via CLI. Do you have any ideas here? It seems setting preWarmedInstanceCount or minimumElasticWorkerCount has no effect on the Always Ready Instances shown in the portal:

This is important for us to be able to trigger an Azure Function behind a VNet