feat(template): Adds provisioning_model to support SPOT preemptible instances

[gcaracuel]

Provider version 4.11.0 added field provisioning_model to scheduling section. This field provides access to https://cloud.google.com/spot-vms

Unfortunately API does not support value to be set to STANDARD when preemptible is true

Error: Error creating instance template: googleapi: Error 400: Invalid value for field 'resource.properties.scheduling.provisioningModel': 'STANDARD'. For preemptible, only allowed provisioning_model value is SPOT., invalid

SPOT instances are a good way to save some costs when applications supports this which is quite common on autoscaling instances.

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