Prevent the use of workload policy for single host nodepools

[FIoannides]

Description

Avoid using workload policy for single host nodepools as recommended by GKE backend team

Issue

ERROR: (gcloud.beta.container.node-pools.create) ResponseError: code=400, message=TPU topology can't be specified with single-host TPU slice pool; please remove the tpu_topology from the node pool creation request if the node pool is intented to run with single-host TPU slice nodes.

Testing

Manually tested a creation of a single host nodepool, don't get the error after this change

[github-actions]

🤖 Hi @FIoannides, I've received your request, and I'm working on it now! You can track my progress in the logs for more details.

[scaliby]

@FIoannides please rebase to the current main. I moved the if statement logic to a dedicated function. I think you're not following this path at this point, but be aware of this change.