minor #5198 Link twig constant function (davidfuhr)

This PR was merged into the 2.3 branch.

Discussion
----------

Link twig constant function

The link was already created but must have been lost in some update.

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | none

Commits
-------

7fb47bf Link twig constant function

best_practices/configuration.rst

@@ -126,7 +126,7 @@ everywhere in your application. When using parameters, they are only available
 from places with access to the Symfony container.
 
 Constants can be used for example in your Twig templates thanks to the
-``constant()`` function:
+`constant() function`_:
 
 .. code-block:: html+jinja