Make use of bean definition overriding more visible

This commit makes the use of bean definition overriding more visible and
prepare for a deprecation of the feature in the next major release.

As of this commit, use of bean definition overriding logs at INFO level.
The previous log level can be restored by setting the
allowBeanDefinitionOverriding flag explicitly on the BeanFactory (or
via the related ApplicationContext).

A number of tests that are using bean overriding on purpose have been
updated to set this flag, which will make them easier to find once we
actually deprecate the feature.

Closes gh-31288

framework-docs/modules/ROOT/pages/core/beans/definition.adoc

@@ -73,7 +73,23 @@ runtime (concurrently with live access to the factory) is not officially support
 lead to concurrent access exceptions, inconsistent state in the bean container, or both.
 ====
 
+[[beans-definition-overriding]]
+== Overriding Beans
 
+Bean overriding is happening when a bean is registered using an identifier that is
+already allocated. While bean overriding is possible, it makes the configuration harder
+to read and this feature will be deprecated in a future release.
+
+To disable bean overriding altogether, you can set the `allowBeanDefinitionOverriding`
+to `false` on the `ApplicationContext` before it is refreshed. In such setup, an
+exception is thrown if bean overriding is used.
+
+By default, the container logs every bean overriding at `INFO` level so that you can
+adapt your configuration accordingly. While not recommended, you can silence those logs
+by setting the `allowBeanDefinitionOverriding` flag to `true`.
+
+NOTE: We acknowledge that overriding beans in a test is convenient, and there is
+explicit support for this. For more details please refer to xref:testing/annotations/integration-spring/annotation-beanoverriding.adoc[this section].
 
 [[beans-beanname]]
 == Naming Beans