feat(api): make Nomad node pool configurable

[chencjcj]

Summary

The Nomad node pool name is currently hardcoded as "default" in the API's orchestrator client . This PR makes it configurable via the NOMAD_NODE_POOL environment variable, enabling deployments that use custom Nomad node pools.

Changes

• Add NomadNodePool config field (NOMAD_NODE_POOL env var, defaults to "default")
• Replace hardcoded "default" pool filter in listNomadNodes with the configurable value
• Pass NOMAD_NODE_POOL from Terraform (var.orchestrator_node_pool) to the API job in both GCP and AWS providers
• Update tests to include the new field

[claude]

Claude Code Review

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[chencjcj]

@dobrac friendly ping — would appreciate your review when you have time. Thanks!

[jakubno]

@chencjcj , thanks for you contribution, but this is currently being reworked and we're moving to different kind of nomad discovery. That should fix this as well (#3176)