Grant vault deployer access to import + manage the rancher engine (#91)

## Why

Wiring the new Rancher token secrets engine into Vault. The deployer registers the plugin (sudo-protected `sys/plugins/catalog`) and configures the engine via the ranchervaultsecret provider, so it needs catalog + engine-path access. Mirrors #88 (gpg).

## Changes

- Add `policies/rancher/admin.yaml` granting the `tf_vault` approle and `woodpecker_terraform_vault` k8s role: catalog sudo on `vault-plugin-secrets-rancher`, and manage on `rancher/{config,service-accounts,roles}`.

## Merge order

Part 1 of 4. Merge before the plugin-import and backend PRs so apply doesn't 403. (Puppet install + this policy first, then import, then backend.)

---------

Co-authored-by: Ben Vincent <neotheo@gmail.com>
Reviewed-on: #91
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

policies/rancher/admin.yaml

@@ -0,0 +1,45 @@
+# Allow the vault deployer to manage the rancher secrets engine: its connection
+# config, seeded (auto-rotated) service-account tokens, and token-minting roles.
+#
+# Scoped to rancher/* only. The plugin-catalog grant needed to import the plugin
+# lives under policies/sys/plugins/catalog/ so a code owner of this policy path
+# cannot grant themselves access outside the rancher mount.
+---
+rules:
+  # Engine connection config.
+  - path: "rancher/config"
+    capabilities:
+      - create
+      - read
+      - update
+      - delete
+  # Seeded, auto-rotated service-account tokens (+ manual rotate).
+  - path: "rancher/service-accounts/*"
+    capabilities:
+      - create
+      - read
+      - update
+      - delete
+      - list
+  - path: "rancher/service-accounts"
+    capabilities:
+      - read
+      - list
+  # Token-minting roles.
+  - path: "rancher/roles/*"
+    capabilities:
+      - create
+      - read
+      - update
+      - delete
+      - list
+  - path: "rancher/roles"
+    capabilities:
+      - read
+      - list
+
+auth:
+  approle:
+    - tf_vault
+  k8s/au/syd1:
+    - woodpecker_terraform_vault

policies/sys/plugins/catalog/rancher.yaml

@@ -0,0 +1,19 @@
+# Allow the vault deployer to import (register/deregister) the rancher secrets
+# plugin in the catalog. sys/plugins/catalog is sudo-protected, so this lives
+# under policies/sys/ where only a sys code owner can grant it — keeping the
+# rancher engine policy (policies/rancher/) scoped to rancher/* paths.
+---
+rules:
+  - path: "sys/plugins/catalog/secret/vault-plugin-secrets-rancher"
+    capabilities:
+      - create
+      - read
+      - update
+      - delete
+      - sudo
+
+auth:
+  approle:
+    - tf_vault
+  k8s/au/syd1:
+    - woodpecker_terraform_vault