feat: parse cluster and jetstream config blocks

src/NATS.Server/Configuration/JetStreamOptions.cs

@@ -0,0 +1,8 @@
+namespace NATS.Server.Configuration;
+
+public sealed class JetStreamOptions
+{
+    public string StoreDir { get; set; } = string.Empty;
+    public long MaxMemoryStore { get; set; }
+    public long MaxFileStore { get; set; }
+}