Grant the terraform_authentik approle / woodpecker_terraform_authentik
k8s role read on kv/data/service/terraform/authentik so the Makefile can
export TF_VAR_authentik_token for the authentik provider.
## Why
terraform-authentik now reads OAuth2 client secrets from Vault (`data.vault_kv_secret_v2`) rather than committing them (terraform-authentik #2). But the `terraform_authentik` approle / `woodpecker_terraform_authentik` k8s role only had the consul-creds policy, so `plan` fails with permission denied on the grafana oauth path.
## Change
Add `policies/kv/service/terraform/authentik.yaml` granting read on `kv/data/kubernetes/namespace/+/default/oauth-credentials` for both the approle and the woodpecker k8s role.
Reviewed-on: #81
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>
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