minor #15048 [Bundles] Add part about resolving parameter values to prepend extension (alexander-schranz)

This PR was merged into the 4.4 branch.

Discussion
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[Bundles] Add part about resolving parameter values to prepend extension

I did run into the following issue: symfony/symfony#40198

As when the `$configs` arrray did contain something like `%kernel.debug%` it did error with:

> Expected "bool", but got "string".

I did debug how symfony is handling this and it seems they are resolving the parameter before here:

https://github.com/symfony/symfony/blob/252f85c2c249da7d8f2a490b57cc71199d51fcc9/src/Symfony/Component/DependencyInjection/Compiler/MergeExtensionConfigurationPass.php#L54-L62

So I think this should also be part of the Prepend Extension Documentation.

Commits
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52ce42f Add part about resolving parameter values to prepend extension

Author: javiereguiluz

bundles/prepend_extension.rst

@@ -82,6 +82,9 @@ in case a specific other bundle is not registered::
 
         // process the configuration of AcmeHelloExtension
         $configs = $container->getExtensionConfig($this->getAlias());
+        // resolve config parameters e.g. %kernel.debug% to boolean value
+        $resolvingBag = $container->getParameterBag();
+        $configs = $resolvingBag->resolveValue($configs);
         // use the Configuration class to generate a config array with
         // the settings "acme_hello"
         $config = $this->processConfiguration(new Configuration(), $configs);