private ManagedChannel getCheckedChannel(final Endpoint endpoint) {
        final ManagedChannel ch = getChannel(endpoint, true);

        if (checkConnectivity(endpoint, ch)) {
            return ch;
        }

        return null;
    }
GRPC RPC client implement.

@author nicholas.jxf
@author jiachun.fjc
jraft-extension/rpc-grpc-impl/src/main/java/com/alipay/sofa/jraft/rpc/impl/GrpcClient.java