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).

resources/secret_backend/consul_root/au/syd1/terraform-enc.hcl

@@ -0,0 +1,7 @@
+key_prefix "infra/terraform/enc/" {
+  policy = "write"
+}
+
+session_prefix "" {
+  policy = "write"
+}