fix: grant vault deployer access to manage the litellm engine (#84)

## Why
Applying the newly-merged litellm mount (#83) failed at apply time with:

```
Error: failed to write litellm config
URL: PUT https://vault.service.consul:8200/v1/litellm/config
Code: 403. * permission denied
```

The deployer identity (`tf_vault` approle / `woodpecker_terraform_vault` k8s role) can enable the mount via `sys/mounts/admin`, but no policy grants it access to the engine's own data paths, so writing the config and roles is denied.

## Changes
- Add `policies/litellm/admin.yaml` granting `create`/`read`/`update`/`delete` on `litellm/config` and `litellm/roles/*` (plus `read`/`list` on `litellm/roles`), assigned to the same auth roles as the other secret-engine admin policies (`tf_vault`, `woodpecker_terraform_vault`).

## Note
The policy attaches to the deployer's auth roles, so it takes effect on the next token issuance — a re-run of the apply (fresh Vault login) will have the permission and can write `litellm/config` and the roles.

Reviewed-on: #84
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

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