It would be useful to have functionality to manipulate KV entries, e.g. to get rid of stale node status entries as seen in a recent customer escalation.

This should be implemented as an admin RPC endpoint or separate RPC service that is only available with node certs (i.e. not via gRPC gateway); we don't want this to be too easily accessible.

The endpoint should take an arbitrary gRPC BatchRequest and pass it through a local sender stack (including at least DistSender but probably also TxnCoordSender), effectively proxying the request for the caller. Transaction support is not necessary, using a single atomic BatchRequest would be sufficient for most uses.

The cockroach debug CLI should at the very least take a Protobuf-encoded BatchRequest, but we may want additional tooling to generate this e.g. from JSON data or CLI command args/flags.