Default number of GCP nodes to 1

What does this MR do?

Lowers the default number of nodes spun up from the QA KubernetesCluster service from 3 to 1.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• [-] Documentation created/updated or follow-up review issue created
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Performance and testing

This change should make clusters faster to spin up since they have less nodes to create.