minor #10373 Mentioned how to redirect and maintain the query string (javiereguiluz)

This PR was merged into the 2.8 branch.

Discussion
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Mentioned how to redirect and maintain the query string

This fixes symfony/symfony#27482.

Commits
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71d6ab1 Mentioned how to redirect and maintain the query string

Author: javiereguiluz

controller.rst

@@ -176,6 +176,9 @@ and ``redirect()`` methods::
         // redirects to a route with parameters
         return $this->redirectToRoute('blog_show', array('slug' => 'my-page'));
 
+        // redirects to a route and mantains the original query string parameters
+        return $this->redirectToRoute('blog_show', $request->query->all());
+
         // redirects externally
         return $this->redirect('http://symfony.com/doc');
     }