feat: 添加多语言客户端 Docker 支持

- 新增 .NET 客户端 SDK 和 demo 项目
- 添加 Go/Node.js/Python/.NET/SpringBoot2 的 Dockerfile
- Go demo 支持从环境变量读取配置
- 创建 README_DOCKERFILE.md 文档说明 Docker 使用方法
- 更新根目录 README.md 标记 .NET 客户端为已支持

kenaito-conf-dotnet-client-demo/Program.cs

@@ -0,0 +1,52 @@
+using Kenaito.Conf.Client;
+
+var config = new Config
+{
+    BaseUrl = "http://localhost:8080",
+    AppName = "kenaito-springboot-demo",
+    Env = "daily",
+    Version = "latest",
+    SyncInterval = 10,
+    CacheDir = "."
+};
+
+var client = new Client(config);
+
+client.OnChange(changed =>
+{
+    Console.WriteLine("Config changed:");
+    foreach (var kv in changed)
+    {
+        Console.WriteLine($"  {kv.Key} = {kv.Value}");
+    }
+});
+
+await client.StartAsync();
+
+Console.WriteLine("Current configs:");
+foreach (var kv in client.GetAll())
+{
+    Console.WriteLine($"  {kv.Key} = {kv.Value}");
+}
+
+var dbHost = client.Get("database.host");
+Console.WriteLine($"\ndatabase.host = {dbHost}");
+
+Console.WriteLine("\nListening for config changes... (press Ctrl+C to stop)");
+var cts = new CancellationTokenSource();
+Console.CancelKeyPress += (s, e) =>
+{
+    e.Cancel = true;
+    cts.Cancel();
+};
+
+try
+{
+    await Task.Delay(Timeout.Infinite, cts.Token);
+}
+catch (TaskCanceledException)
+{
+}
+
+Console.WriteLine("\nShutting down...");
+client.Stop();