Update sigs.k8s.io/gateway-api to v1.2.0-rc1

Co-authored-by: Kevin Pollet <pollet.kevin@gmail.com>

docs/content/migration/v3.md

@@ -78,7 +78,7 @@ Please use the `disableClusterScopeResources` option instead to avoid cluster sc
 
 ## v3.1 to v3.2
 
-### Kubernetes Gateway Provider RBACs
+### Kubernetes Gateway Provider Standard Channel
 
 Starting with v3.2, the Kubernetes Gateway Provider now supports [GRPCRoute](https://gateway-api.sigs.k8s.io/api-types/grpcroute/).
 
@@ -103,3 +103,34 @@ the `grcroutes` and `grpcroutes/status` rights have to be added.
       - update
   ...
 ```
+
+### Kubernetes Gateway Provider Experimental Channel
+
+!!! warning "Breaking changes"
+
+    Because of a breaking change introduced in Kubernetes Gateway [v1.2.0-rc1](https://github.com/kubernetes-sigs/gateway-api/releases/tag/v1.2.0-rc1),
+    Traefik v3.2 only supports Kubernetes Gateway v1.2.x when experimental channel features are enabled.
+
+Starting with v3.2, the Kubernetes Gateway Provider now supports [BackendTLSPolicy](https://gateway-api.sigs.k8s.io/api-types/backendtlspolicy/).
+
+Therefore, in the corresponding RBACs (see [KubernetesGateway](../reference/dynamic-configuration/kubernetes-gateway.md#rbac) provider RBACs),
+the `backendtlspolicies` and `backendtlspolicies/status` rights have to be added.
+
+```yaml
+  ...
+  - apiGroups:
+      - gateway.networking.k8s.io
+    resources:
+      - backendtlspolicies
+    verbs:
+      - get
+      - list
+      - watch
+  - apiGroups:
+      - gateway.networking.k8s.io
+    resources:
+      - backendtlspolicies/status
+    verbs:
+      - update
+  ...
+```