Terraform GCE should set groups update_policy

[justinsb]

/kind bug

As reported here:
#17229 (comment)

We're also running into an issue where the instance groups update_policy aren't set, and for unclear reasons this results in effective type = "PROACTIVE" configuration for one cluster (but not the other) causing an immediate restart of all three control planes at once and thus some downtime. I believe it would be beneficial to explicitly set the update policy to prevent this.

[justinsb]

I looked around and couldn't find the cause here, particularly of the different behavior. I found some hints that if autoscaling is enabled the default might be different, but this shouldn't apply to control planes.

Because I don't yet have clarity on this, I propose we set the update_policy for all GCE users (terraform and non-terraform), but do so in the next minor version of kOps.