minor #9446 Include a reference to the namespace option (guilhermednt)

This PR was merged into the 3.4 branch.

Discussion
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Include a reference to the namespace option

Currently the Symfony doc doesn't appear to mention the `namespace` option for Doctrine's cache drivers that is available [since DoctrineBundle v1.3.0](doctrine/DoctrineBundle@d211072)

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Commits
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594a156 Include a reference to the namespace option

Author: javiereguiluz

reference/configuration/doctrine.rst

@@ -134,18 +134,21 @@ Full Default Configuration
                             port:                 ~
                             instance_class:       ~
                             class:                ~
+                            namespace:            ~
                         metadata_cache_driver:
                             type:                 array # Required
                             host:                 ~
                             port:                 ~
                             instance_class:       ~
                             class:                ~
+                            namespace:            ~
                         result_cache_driver:
                             type:                 array # Required
                             host:                 ~
                             port:                 ~
                             instance_class:       ~
                             class:                ~
+                            namespace:            ~
                         connection:           ~
                         class_metadata_factory_name:  Doctrine\ORM\Mapping\ClassMetadataFactory
                         default_repository_class:  Doctrine\ORM\EntityRepository