Ensure that when a replace operation is done on the metadata-only path metadata is replaced, ensure that metadata can be received and is persisted over a device reboot.

• Build a protobuf message, marshal, and base64 encode the result.
• Make a gNMI Set request for the path /@/openconfig-metadata:protobuf-metadata whose value is the base64 encoded result.
• Make a gNMI Get for the same path to retrieve the value back.
• Validate that the returned value can be base64 decoded, unmarshaled, and matches the original protobuf.

No configuration coverage.

• /@/openconfig-metadata:protobuf-metadata

Note: WBB implementations need not support this annotation at paths deeper than the root (i.e., a configuration that contains openconfig-metadata:protobuf-metadata at any level other than under the root can be rejected). The WBB device implementation can map this to an internal path to store the configuration.