feat: add additional_helm_values variable for custom Helm configuration

[NickHilton]

Summary

Add additional_helm_values variable to allow users to pass custom Helm values to the Langfuse chart.

Use Case

This enables configuring:

• Node selectors (e.g., GKE Spot VMs for cost optimization)
• Tolerations
• Resource limits/requests
• Any other Helm chart values not exposed as module variables

Example

module "langfuse" {
  source = "github.com/langfuse/langfuse-terraform-gcp"
  
  domain = "langfuse.example.com"
  
  additional_helm_values = <<-EOT
    langfuse:
      web:
        nodeSelector:
          cloud.google.com/gke-spot: "true"
        tolerations:
          - key: cloud.google.com/gke-spot
            operator: Equal
            value: "true"
            effect: NoSchedule
  EOT
}

Changes

• Add additional_helm_values variable (string, default "")
• Update helm_release.langfuse to include additional values using compact() to filter empty strings

[CLAassistant]

All committers have signed the CLA.