minor #19738 [DependencyInjection] Updating prepend extension capabilities (yceruto)

This PR was merged into the 7.1 branch.

Discussion
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[DependencyInjection] Updating prepend extension capabilities

Fixes #19735

I'm also suggesting removing the append example in the prepend extension method. As explained in PR symfony/symfony#52843 and related issues, it's flawed and should be discouraged from the official documentation.

I'll create a new PR to target the lower branch and remove it there too.

Commits
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25c5adf Updating prepend extension capabilities

Author: javiereguiluz

bundles/prepend_extension.rst

@@ -171,13 +171,22 @@ method::
             $containerBuilder->prependExtensionConfig('framework', [
                 'cache' => ['prefix_seed' => 'foo/bar'],
             ]);
+
+            // prepend config from a file
+            $containerConfigurator->import('../config/packages/cache.php');
         }
     }
 
 .. note::
 
     The ``prependExtension()`` method, like ``prepend()``, is called only at compile time.
 
+.. deprecated:: 7.1
+
+    The :method:`Symfony\\Component\\DependencyInjection\\Loader\\Configurator\\ContainerConfigurator::import`
+    method behavior was modified in Symfony 7.1 to prepend config instead of appending. This behavior change only
+    affects to the ``prependExtension()`` method.
+
 Alternatively, you can use the ``prepend`` parameter of the
 :method:`Symfony\\Component\\DependencyInjection\\Loader\\Configurator\\ContainerConfigurator::extension`
 method::