Add response stream to context in DownloadHttpFile

In DownloadHttpFile.cs, context data now includes response content's file stream. Changes to DefaultDownloadableManager.cs simplify the return statement when no provider is found, directly returning an empty array.

src/modules/Elsa.Http/Activities/DownloadHttpFile.cs

@@ -150,6 +150,7 @@ public class DownloadHttpFile : Activity<HttpFile>, IActivityPropertyDefaultValu
             var responseContentHeaders = new HttpHeaders(response.Content.Headers);
 
             context.Set(Response, response);
+            context.Set(ResponseContent, file?.Stream);
             context.Set(Result, file);
             context.Set(StatusCode, statusCode);
             context.Set(ResponseHeaders, responseHeaders);

src/modules/Elsa.Http/Services/DefaultDownloadableManager.cs

@@ -24,7 +24,7 @@ public class DefaultDownloadableManager : IDownloadableManager
         var provider = _providers.FirstOrDefault(x => x.GetSupportsContent(content));
 
         if (provider == null)
-            return Enumerable.Empty<Func<ValueTask<Downloadable>>>();
+            return [];
 
         options ??= new();
         var context = new DownloadableContext(this, content, options, cancellationToken);