Reverts the temporary removal in #129. The ghp config KV path
kv/data/service/vault/au/syd1/secret_backend/ghp/config (key admin_token)
is now seeded, and the ghp service secret carries the matching service_token,
so data.vault_kv_secret_v2.config resolves and the backend + role can be
created.
Restore config/ghp_secret_backend/ghp.yaml.
Restore config/ghp_secret_backend_role/ghp/agent.yaml.
Net diff vs master is exactly the re-addition of those two files (mirror-inverse
of #129). Final step of the remove -> grant -> seed -> add-back sequence.
unkin-agent