OST poc create user request

1. ost.cs

private static string baseUrl = "https://playgroundapi.ost.com";
private static string key = "xxx";

var name = "apiuser";
var timestamp = DateTimeOffset.UtcNow.ToUnixTimeSeconds().ToString();

var request = $"/users/create?api_key={key}&name={name}&request_timestamp={timestamp}";
var signature = Sign(request);

var values = new Dictionary<string, string>
{
    { "api_key", key },
    { "name", name },
    { "request_timestamp", timestamp },
    { "signature", signature }
};

var url = $"{baseUrl}{request}&signature={signature}";

var content = new FormUrlEncodedContent(values);
var response = await client.PostAsync(url, content);

2. ost-api-proposal.cs

private static string baseUrl = "https://playgroundapi.ost.com";
private static string apiKey = "xxx";

var name = "Test User";
var timestamp = DateTimeOffset.UtcNow.ToUnixTimeSeconds().ToString();

var endpoint = $"/users/create";
var signature = Sign(apiKey, timestamp);

var values = new Dictionary<string, string>
{
    { "name", name },
    { "signature", signature }
};

var url = $"{BaseUrl}{request}";

var content = new FormUrlEncodedContent(values);
var response = await Client.PostAsync(url, content);