Add support for custom headers in HTTP requests

Enhanced HTTP request handling by adding support for dynamically including custom headers from the `request.Headers` collection. Implemented a null check to ensure robustness and prevent null reference exceptions when processing headers. This change improves flexibility and customization of HTTP requests.

src/ReC.Application/RecActions/Commands/InvokeRecActionCommand.cs

@@ -57,6 +57,10 @@ public class InvokeRecActionCommandHandler(
             );
         }
 
+        if (request.Headers is not null)
+            foreach (var header in request.Headers)
+                httpReq.Headers.Add(header.Key, header.Value);
+
         using var response = await http.SendAsync(httpReq, cancel);
         var body = await response.Content.ReadAsStringAsync(cancel);
         var headers = response.Headers.ToDictionary();