minor #11157 [REFACTOR] Messenger - Serializer groups (Guikingone)

This PR was submitted for the 4.2 branch but it was squashed and merged into the 4.3 branch instead (closes #11157).

Discussion
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[REFACTOR] Messenger - Serializer groups

Hi everyone,

I've faced some problems yesterday due to groups definition (mainly about embedded objects) and I think it could be a good idea to add a tip (or even a note?) about the `groups` usage.

Any idea?

Thanks :)

Commits
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bea832f [REFACTOR] Messenger - Serializer groups

Author: javiereguiluz

components/messenger.rst

@@ -139,6 +139,11 @@ through the transport layer, use the ``SerializerStamp`` stamp::
         ]))
     );
 
+.. note::
+
+    As the groups are applied to the whole message,
+    be sure to define the group for every embedded object. 
+
 At the moment, the Symfony Messenger has the following built-in envelope stamps:
 
 #. :class:`Symfony\\Component\\Messenger\\Stamp\\SerializerStamp`,