Add StreamableHttpHandler and WithHttpTransport (#291)

* Simplify ModelContextProtocol.AspNetCore README

* Add StreamableHttpHandler

* Use "docker info" in CheckIsDockerAvailable

* Call WithHttpTransport in samples, tests and README

* Cleanup test namespaces

* Add CanConnect_WithMcpClient_AfterCustomizingRoute test

* Simplify relative URI handling

* Handle request made directly to the MapMcp route pattern

* Add Messages_FromNewUser_AreRejected test

* Fix README

* Shorten UserIdClaim ValueTuple names

* Remove MaxReconnectAttempts and ReconnectDelay from SseClientTransportOptions

- Add proper AdditionalHeaders support

src/ModelContextProtocol.AspNetCore/HttpServerTransportOptions.cs

@@ -0,0 +1,24 @@
+using Microsoft.AspNetCore.Http;
+using ModelContextProtocol.Server;
+
+namespace ModelContextProtocol.AspNetCore;
+
+/// <summary>
+/// Configuration options for <see cref="M:McpEndpointRouteBuilderExtensions.MapMcp"/>.
+/// which implements the Streaming HTTP transport for the Model Context Protocol.
+/// See the protocol specification for details on the Streamable HTTP transport. <see href="https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#streamable-http"/>
+/// </summary>
+public class HttpServerTransportOptions
+{
+    /// <summary>
+    /// Gets or sets an optional asynchronous callback to configure per-session <see cref="McpServerOptions"/>
+    /// with access to the <see cref="HttpContext"/> of the request that initiated the session.
+    /// </summary>
+    public Func<HttpContext, McpServerOptions, CancellationToken, Task>? ConfigureSessionOptions { get; set; }
+
+    /// <summary>
+    /// Gets or sets an optional asynchronous callback for running new MCP sessions manually.
+    /// This is useful for running logic before a sessions starts and after it completes.
+    /// </summary>
+    public Func<HttpContext, IMcpServer, CancellationToken, Task>? RunSessionHandler { get; set; }
+}