[RunsOn] Limit instance families to standard types

[Nuru]

what

• Limit RunsOn instances to "standard" instance families

why

• Non-standard instances are subject to service quotas that can be as low as zero by default. We want to be able to launch a lot of instances, and need a high quota, so we should stick to the standard instances that share the same single quota we have already increased.

[mergify]

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