fix: grant vault deployer access to manage the litellm engine

Applying the litellm mount failed with 403 permission denied on
PUT litellm/config: the deployer identity (tf_vault approle /
woodpecker_terraform_vault k8s role) could enable the mount via
sys/mounts/admin but had no policy covering the engine's own data paths.

Add a litellm/admin policy granting create/read/update/delete on
litellm/config and litellm/roles/*, assigned to the same auth roles as the
other secret-engine admin policies.

policies/litellm/admin.yaml

@@ -0,0 +1,26 @@
+# Allow management of the LiteLLM secrets engine (config and roles)
+---
+rules:
+  - path: "litellm/config"
+    capabilities:
+      - create
+      - update
+      - read
+      - delete
+  - path: "litellm/roles/*"
+    capabilities:
+      - create
+      - update
+      - delete
+      - read
+      - list
+  - path: "litellm/roles"
+    capabilities:
+      - read
+      - list
+
+auth:
+  approle:
+    - tf_vault
+  k8s/au/syd1:
+    - woodpecker_terraform_vault