Bring the litellm plugin under terraform management like the gpg one, using the new plugin-import module (#89).
## Why
The litellm plugin was registered **manually** before terraform owned the catalog. If we just add it to `config/plugins/`, the first apply tries to *create* a catalog entry that already exists and fails. So its state must be imported first.
## Changes
- Add `config/plugins/vault-plugin-secrets-litellm.yaml` (`sha256` = released **v0.1.1** openbao binary from the RPM Puppet installs).
## Manual pre-step (before apply)
Import the existing registration into state, and verify the sha matches the live catalog:
```sh
cd environments/au/syd1
# confirm the live sha first:
bao read sys/plugins/catalog/secret/vault-plugin-secrets-litellm
# import into state:
terragrunt import \
'module.plugin["vault-plugin-secrets-litellm"].vault_plugin.this' \
secret/vault-plugin-secrets-litellm
```
If the live sha differs from the yaml, update the yaml to match (or expect a benign re-register to the on-disk v0.1.1 sha). Needs the deployer's plugin-catalog access (#88, already merged).
Reviewed-on: #90
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>
