Hypernode abnormal metrics should increase when RPC endpoint is unavailable.

[kernelpanic9]

Example: When Klaytn node was shutdown, none of the following Hypernode metrics were increasing (see below).
Most likely Unavailable or NotFound counter should have been increasing, when peer blockchain node is unavailable.
It would be possible to set up alerting based on that.

grpc_server_handled_total{grpc_code="Aborted",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="AlreadyExists",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="Canceled",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="DataLoss",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="DeadlineExceeded",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="FailedPrecondition",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="Internal",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="InvalidArgument",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="NotFound",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="OK",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="OutOfRange",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="PermissionDenied",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="ResourceExhausted",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="Unauthenticated",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="Unavailable",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="Unimplemented",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0
grpc_server_handled_total{grpc_code="Unknown",grpc_method="ServerReflectionInfo",grpc_service="grpc.reflection.v1alpha.ServerReflection",grpc_type="bidi_stream"} 0