Scope rancher policy to rancher/*; move catalog grant under sys/plugins

Addresses review: a policy's directory should be the base of the paths it
grants, so a code owner of one policy path cannot grant themselves access
elsewhere (e.g. sys or approle).

- policies/rancher/admin.yaml now grants only rancher/{config,service-accounts,
  roles}.
- Move the sudo-protected plugin-catalog grant to
  policies/sys/plugins/catalog/rancher.yaml (base path sys/plugins/catalog/),
  owned by a sys code owner.

policies/rancher/admin.yaml

@@ -1,21 +1,11 @@
-# Allow the vault deployer to import the rancher plugin and manage its engine
-# (config, seeded service accounts, and roles).
+# Allow the vault deployer to manage the rancher secrets engine: its connection
+# config, seeded (auto-rotated) service-account tokens, and token-minting roles.
 #
-# terraform-vault registers the plugin itself (vault_plugin -> sys/plugins/catalog,
-# a sudo-protected path) and manages the engine via the ranchervaultsecret
-# provider, so the deployer needs catalog access on top of the mount access it
-# already has (sys/mounts/*). Without this, apply 403s on the plugin
-# registration and on rancher/{config,service-accounts,roles} writes.
+# 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:
-  # Import / register (and deregister) the rancher plugin in the catalog.
-  - path: "sys/plugins/catalog/secret/vault-plugin-secrets-rancher"
-    capabilities:
-      - create
-      - read
-      - update
-      - delete
-      - sudo
   # Engine connection config.
   - path: "rancher/config"
     capabilities: