Add tagging support for google_container_cluster using resource_labels

[yhengly]

Summary

Adds support for tagging google_container_cluster resources. This resource uses resource_labels as its tag attribute instead of the standard labels used by most GCP resources, which required introducing a per-resource-type tag attribute override mechanism.

Problem

Yor maps each Terraform provider to a single tag attribute name via ProviderToTagAttribute (e.g., google → labels). However, google_container_cluster uses resource_labels for its tags, not labels. Without this change, Yor either skips the resource or writes tags to the wrong attribute.

Changes

• src/terraform/structure/terraform_block.go — Added ResourceTypeToTagAttribute map to override the provider-level tag attribute for specific resource types (google_container_cluster → resource_labels)
• src/terraform/structure/terraform_parser.go — Modified getTagAttributeByResourceType() to check the resource-type override map before falling back to the provider default
• src/terraform/structure/tf_taggable.go — Added google_container_cluster to TfTaggableResourceTypes
• tests/terraform/resources/gke/main.tf — Test fixture with tagged and untagged google_container_cluster resources
• src/terraform/structure/terraform_parser_test.go — Parser test verifying taggability, correct attribute name (resource_labels), and tag extraction
• src/terraform/structure/terraform_block_test.go — Block tests verifying IsGCPBlock() detection and ResourceTypeToTagAttribute override correctness

How It Works

getTagAttributeByResourceType("google_container_cluster")
  → checks ResourceTypeToTagAttribute → finds "resource_labels" → returns it

getTagAttributeByResourceType("google_storage_bucket")
  → checks ResourceTypeToTagAttribute → not found
  → falls back to ProviderToTagAttribute["google"] → returns "labels"

Testing

• Functional test: go run main.go tag -d tests/terraform/resources/gke --dry-run -o json confirms both resources are detected and tagged under resource_labels
• Full regression: scanning tests/terraform/resources/ (67 resources across AWS/GCP/modules) completes with zero errors
• Backward-compatible: all existing resources continue using their provider-level tag attribute mapping

Extensibility

Future GCP resources with non-standard tag attributes (e.g., google_container_node_pool also uses resource_labels) can be added with a single line in the ResourceTypeToTagAttribute map.