Add auth and state access for terraform-rancher

Mirrors the terraform-authentik runner setup (#78/#81/#82) for the new
terraform-rancher repo, which manages Rancher's Authentik OIDC auth via the
rancher2 provider.

- AppRole terraform_rancher + k8s auth role woodpecker_terraform_rancher.
- Consul secret backend role + ACL policy granting write to the
  infra/terraform/rancher/ state prefix.
- Vault policies: read the Rancher admin API token
  (kv/service/terraform/rancher) and the keycloakoidc client secret
  (kv/kubernetes/namespace/cattle-system/default/oauth-credentials), plus the
  consul_root state creds.

config/auth_approle_role/approle/terraform_rancher.yaml

@@ -0,0 +1,9 @@
+token_ttl: 120
+token_max_ttl: 120
+bind_secret_id: false
+token_bound_cidrs:
+  - "10.10.12.200/32"
+  - "198.18.25.102/32"
+  - "198.18.26.91/32"
+  - "198.18.27.40/32"
+use_deterministic_role_id: true