[Cache] Document using DSN with PDOAdapter

cache.rst

@@ -133,12 +133,7 @@ Some of these adapters could be configured via shortcuts.
                 default_psr6_provider: 'app.my_psr6_service'
                 default_redis_provider: 'redis://localhost'
                 default_memcached_provider: 'memcached://localhost'
-                default_pdo_provider: 'app.my_pdo_service'
-
-        services:
-            app.my_pdo_service:
-                class: \PDO
-                arguments: ['pgsql:host=localhost']
+                default_pdo_provider: 'pgsql:host=localhost'
 
     .. code-block:: xml
 
@@ -159,24 +154,17 @@ Some of these adapters could be configured via shortcuts.
                     default-psr6-provider="app.my_psr6_service"
                     default-redis-provider="redis://localhost"
                     default-memcached-provider="memcached://localhost"
-                    default-pdo-provider="app.my_pdo_service"
+                    default-pdo-provider="pgsql:host=localhost"
                 />
             </framework:config>
-
-            <services>
-                <service id="app.my_pdo_service" class="\PDO">
-                    <argument>pgsql:host=localhost</argument>
-                </service>
-            </services>
         </container>
 
     .. code-block:: php
 
         // config/packages/cache.php
-        use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;
         use Symfony\Config\FrameworkConfig;
 
-        return static function (FrameworkConfig $framework, ContainerConfigurator $container): void {
+        return static function (FrameworkConfig $framework): void {
             $framework->cache()
                 // Only used with cache.adapter.filesystem
                 ->directory('%kernel.cache_dir%/pools')
@@ -185,15 +173,14 @@ Some of these adapters could be configured via shortcuts.
                 ->defaultPsr6Provider('app.my_psr6_service')
                 ->defaultRedisProvider('redis://localhost')
                 ->defaultMemcachedProvider('memcached://localhost')
-                ->defaultPdoProvider('app.my_pdo_service')
-            ;
-
-            $container->services()
-                ->set('app.my_pdo_service', \PDO::class)
-                ->args(['pgsql:host=localhost'])
+                ->defaultPdoProvider('pgsql:host=localhost')
             ;
         };
 
+.. versionadded:: 7.1
+
+    Using a DSN as the provider for the PDO adapter was introduced in Symfony 7.1.
+
 .. _cache-create-pools:
 
 Creating Custom (Namespaced) Pools