Expose LATENCY LATEST to the python client

[ctandon11]

Description

Give the python client access to the Redis command LATENCY LATEST by exposing it
through the Pybindings.

Justification

The user will be able to access the latest latency events logged.

Implementation Strategy

LATENCY LATEST will be an AddressAtCommand.

Note: This function returns an array where each element is a four elements array representing the event's name, timestamp, latest and all-time latency measurements. Like ClusterInfoCommand, we should implement a LatencyLatestCommand subclass of AddressAtCommand that contains a separate parsing function, i.e. std::vector<std::vector<std::string>> LatencyLatestCommand::parse(CommandReply reply).

The implementation will look something like this in client.cpp:

std::vector<std::vector<std::string>> Client::latency_latest(std::string address)
{
    std::string host = address.substr(0, address.find(":"));
    uint64_t port = std::stoul(address.substr(address.find(":") + 1),
                                nullptr, 0);
    if (host.empty() or port == 0){
        throw std::runtime_error(std::string(address) +
                                 "is not a valid database node address.");
    }
    LatencyLatestCommand cmd;
    cmd.set_exec_address_port(host, port);

    cmd.add_field("LATENCY");
    cmd.add_field("LATEST");

    CommandReply reply = _run(cmd);
    if (reply.has_error() > 0)
        throw std::runtime_error("LATENCY RESET command failed");


    return cmd.parse(reply);
}

This functionality then needs to be exposed through the Pybindings and pyclient.cpp file to the python client layer. For unit testing, make sure an invalid address throws an error.