feat: parse cluster and jetstream config blocks

src/NATS.Server/Configuration/GatewayOptions.cs

@@ -0,0 +1,8 @@
+namespace NATS.Server.Configuration;
+
+public sealed class GatewayOptions
+{
+    public string? Name { get; set; }
+    public string Host { get; set; } = "0.0.0.0";
+    public int Port { get; set; }
+}