Adding a new module to dynamically discover GCP Backend Service IDs from GKE Ingress.

When a GKE Ingress controller creates a Global Load Balancer, it generates Backend Services with dynamic, non-deterministic names. This makes it difficult to reference these backends in declarative Terraform code (e.g., for applying Identity-Aware Proxy policies).

This module introduces a Python-based utility that queries the GKE cluster's ingress annotations to resolve the mapping between a Kubernetes Service/Port and the corresponding Google Cloud Backend Service ID.

Key Changes:

External Data Provider: Utilizes the Terraform external provider to execute a specialized Python discovery script.
Python Logic: Implements a robust polling loop with a configurable timeout to wait for the GKE Ingress controller to successfully provision the cloud resources and update the ingress annotations.
Credential Handling: The script automatically handles gcloud container clusters get-credentials to ensure kubectl context is available for the lookup.
Output: Provides the backend_service_id and backend_service_name as standard Terraform outputs for consumption by downstream IAM/IAP modules.

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