/claim #944

Summary

• register the standard gRPC health service on the server
• expose SERVING status for the server and each registered gRPC service
• cover health stream RPCs with the existing auth and recovery interceptors
• add bufconn-based tests for health checks and stream interceptors

Testing

• go test ./www/grpc -run ‘TestHealthCheck|TestHealthCheckWalletService|TestBasicAuthStream|TestGrpcRecoveryStream’\n- go test ./www/grpc