minor #17532 [FrameworkBundle][Messenger] Extend note on routing with support for wildcard routes (brzuchal)

This PR was submitted for the 6.3 branch but it was merged into the 6.2 branch instead.

Discussion
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[FrameworkBundle][Messenger] Extend note on routing with support for wildcard routes

Extend wildcard `'*'` note with information about the usage of namespace wildcards.

Commits
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c4e2655 [Messenger] Extend note on routing with support for wildcard routes

Author: javiereguiluz

messenger.rst

@@ -259,6 +259,11 @@ matched under ``routing`` will still be handled immediately, i.e. synchronously.
 
 .. note::
 
+    You may use ``'App\Message\*'`` combined with valid namespace. The wildcard
+    at the end will act as a routing for all messages within the matching namespace.
+    The wildcard can follow any valid namespace but has to be placed at the end.
+    This is useful to route all classes sharing the same namespace to the same transport.
+
     You may use ``'*'`` as the message class. This will act as a default routing
     rule for any message not matched under ``routing``. This is useful to ensure
     no message is handled synchronously by default.