feat: add Kubernetes Gateway API v1 resources and data sources

[Ret2Me]

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Rollback Plan

If a change needs to be reverted, we will publish an updated version of the library.

Changes to Security Controls

No changes to security controls. The new resources are read/write wrappers around
existing Kubernetes Gateway API objects and follow the same RBAC model as other
namespaced resources in this provider.

Description

Adds support for the Kubernetes Gateway API
(gateway.networking.k8s.io), which is the standard successor to the Ingress API
for managing L4/L7 traffic routing. All resources target the v1 API group
(sigs.k8s.io/gateway-api v1.5.1).

New resources and data sources:

• kubernetes_gateway_class_v1 / data.kubernetes_gateway_class_v1
• kubernetes_gateway_v1 / data.kubernetes_gateway_v1
• kubernetes_http_route_v1 / data.kubernetes_http_route_v1
• kubernetes_grpc_route_v1 / data.kubernetes_grpc_route_v1
• kubernetes_tls_route_v1 / data.kubernetes_tls_route_v1
• kubernetes_reference_grant_v1 / data.kubernetes_reference_grant_v1
• kubernetes_backend_tls_policy_v1 / data.kubernetes_backend_tls_policy_v1
• kubernetes_listener_set_v1 / data.kubernetes_listener_set_v1

Key features covered:

• path/header/method/query matching
• all HTTPRoute filter
• types (CORS, RequestMirror, RequestRedirect, URLRewrite, header modifiers)
• session persistence (Cookie with CookieConfig, Header)
• retry with status codes
• per-rule timeouts
• weighted backend splits
• TLS termination and passthrough
• cross-namespace routing via ReferenceGrant, and BackendTLSPolicy with
  SubjectAltNames (Hostname and URI).

All resources support terraform import via namespace/name.

Acceptance tests

• Have you added an acceptance test for the functionality being added?
• Have you run the acceptance tests on this branch?

Tested against a KinD cluster with Gateway API CRDs installed:

kind create cluster --config=./.github/config/acceptance_tests_kind_config.yaml
kubectl apply -f https://github.com/kubernetes-sigs/gateway-api/releases/download/v1.2.1/standard-install.yaml

Output from acceptance testing:

$ make testacc TESTARGS='-run=TestAccKubernetesGatewayClassV1|TestAccKubernetesGatewayV1|TestAccKubernetesHTTPRouteV1|TestAccKubernetesGRPCRouteV1|TestAccKubernetesTLSRouteV1|TestAccKubernetesReferenceGrantV1|TestAccKubernetesBackendTLS
PolicyV1|TestAccKubernetesListenerSetV1|TestAccKubernetesGatewayAPI'

--- PASS: TestAccKubernetesGatewayClassV1_basic (3.91s)
--- PASS: TestAccKubernetesGatewayV1_basic (3.06s)
--- PASS: TestAccKubernetesHTTPRouteV1_basic (3.33s)
--- PASS: TestAccKubernetesHTTPRouteV1_complexFilters (9.14s)
--- PASS: TestAccKubernetesGRPCRouteV1_basic (3.65s)
--- PASS: TestAccKubernetesGRPCRouteV1_complex (8.21s)
--- PASS: TestAccKubernetesTLSRouteV1_basic (6.85s)
--- PASS: TestAccKubernetesReferenceGrantV1_basic (6.16s)
--- PASS: TestAccKubernetesBackendTLSPolicyV1_basic (6.69s)
--- PASS: TestAccKubernetesListenerSetV1_basic (6.90s)
--- PASS: TestAccKubernetesGatewayAPI_HTTPSRedirect (2.74s)
--- PASS: TestAccKubernetesGatewayAPI_CanaryDeployment (8.64s)
--- PASS: TestAccKubernetesGatewayAPI_PathBasedMicroservices (5.12s)
--- PASS: TestAccKubernetesGatewayAPI_GRPCRoutingAdvanced (2.45s)
--- PASS: TestAccKubernetesGatewayAPI_MultiTenantFull (10.98s)
--- PASS: TestAccKubernetesGatewayAPIStack_crossNamespace (10.93s)
ok    github.com/hashicorp/terraform-provider-kubernetes/kubernetes   42.31s

Release Note

FEATURES:

• New resource: kubernetes_gateway_class_v1
• New resource: kubernetes_gateway_v1
• New resource: kubernetes_http_route_v1
• New resource: kubernetes_grpc_route_v1
• New resource: kubernetes_tls_route_v1
• New resource: kubernetes_reference_grant_v1
• New resource: kubernetes_backend_tls_policy_v1
• New resource: kubernetes_listener_set_v1
• New data source: kubernetes_gateway_class_v1
• New data source: kubernetes_gateway_v1
• New data source: kubernetes_http_route_v1
• New data source: kubernetes_grpc_route_v1
• New data source: kubernetes_tls_route_v1
• New data source: kubernetes_reference_grant_v1
• New data source: kubernetes_backend_tls_policy_v1
• New data source: kubernetes_listener_set_v1

References

• Gateway API specification: https://gateway-api.sigs.k8s.io/
• Gateway API Go module: https://pkg.go.dev/sigs.k8s.io/gateway-api/apis/v1
• Upstream issue tracking Gateway API support: Gateway API v1.0 #2474

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Note: Separately I've got a set of manual test configs (Terraform + kubectl script)
that verify all resources live including CORS, canaries, TLS passthrough, SANs
in BackendTLSPolicy, cross‑namespace routing, and more.

Happy to share if it helps with review or examples.

Closes: #2474

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[Ret2Me]

Sorry for delivering everything as one commit. I realize that's messy.

The problem is the code is from an internal much bigger project repo, and I can't share the original commit history.
This "stash" was the only practical way to get you the current working version.

Thanks for your understanding and sorry again for the hassle.

[Ret2Me]

Also, your Atlassian integration pipeline is broken, it's calling a deprecated endpoint.

API call GET /rest/api/3/search failed (410): The requested API has been removed. Please migrate to /rest/api/3/search/jql