Add conceptual docs on accessing HttpContext (#771)

* Add doc with sample on accessing HttpContext
* Apply suggestions from PR review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

docs/concepts/httpcontext/samples/Tools/ContextTools.cs

@@ -0,0 +1,28 @@
+using ModelContextProtocol.Server;
+using System.ComponentModel;
+
+namespace HttpContext.Tools;
+
+// <snippet_AccessHttpContext>
+public class ContextTools(IHttpContextAccessor httpContextAccessor)
+{
+    [McpServerTool(UseStructuredContent = true)]
+    [Description("Retrieves the HTTP headers from the current request and returns them as a JSON object.")]
+    public object GetHttpHeaders()
+    {
+        var context = httpContextAccessor.HttpContext;
+        if (context == null)
+        {
+            return "No HTTP context available";
+        }
+
+        var headers = new Dictionary<string, string>();
+        foreach (var header in context.Request.Headers)
+        {
+            headers[header.Key] = string.Join(", ", header.Value.ToArray());
+        }
+
+        return headers;
+    }
+// </snippet_AccessHttpContext>
+}