Add terraform-enc auth, consul state role, and encapi token grant

The new terragrunt-enc repo manages all encapi ENC data via Terraform and
needs its own Vault/Consul plumbing, mirroring terraform-git/terraform-incus:
CI auth, isolated consul state, and read access to the ENCAPI_WRITE_TOKEN.

- Add approle role terraform_enc and k8s auth role woodpecker_terraform_enc
  (bound to the terraform-enc SA in the woodpecker namespace).
- Add consul secret backend role + ACL rules granting write on
  infra/terraform/enc/ for its terragrunt state, plus a policy letting both
  auth roles read consul_root/au/syd1/creds/terraform-enc.
- Grant both auth roles read on
  kv/data/kubernetes/namespace/encapi/default/environment (ENCAPI_WRITE_TOKEN).

policies/consul_root/au/syd1/creds/terraform-enc.yaml

@@ -0,0 +1,14 @@
+# Allow the terragrunt-enc runner to generate credentials for the
+# terraform-enc role in consul (used to lock/write its terragrunt state under
+# infra/terraform/enc/ on the consul backend).
+---
+rules:
+  - path: "consul_root/au/syd1/creds/terraform-enc"
+    capabilities:
+      - read
+
+auth:
+  approle:
+    - terraform_enc
+  k8s/au/syd1:
+    - woodpecker_terraform_enc