minor symfony#21570 [Messenger] Add MessageSentToTransportsEvent (alexandre-daubois)

This PR was merged into the 7.4 branch.

Discussion
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[Messenger] Add `MessageSentToTransportsEvent`

Fix symfony#21536

Commits
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c7aa657 [Messenger] Add `MessageSentToTransportsEvent`

Author: javiereguiluz

messenger.rst

@@ -3394,6 +3394,7 @@ In addition to middleware, Messenger also dispatches several events. You can
 of the process. For each, the event class is the event name:
 
 * :class:`Symfony\\Component\\Messenger\\Event\\SendMessageToTransportsEvent`
+* :class:`Symfony\\Component\\Messenger\\Event\\MessageSentToTransportsEvent`
 * :class:`Symfony\\Component\\Messenger\\Event\\WorkerMessageFailedEvent`
 * :class:`Symfony\\Component\\Messenger\\Event\\WorkerMessageHandledEvent`
 * :class:`Symfony\\Component\\Messenger\\Event\\WorkerMessageReceivedEvent`
@@ -3403,6 +3404,16 @@ of the process. For each, the event class is the event name:
 * :class:`Symfony\\Component\\Messenger\\Event\\WorkerStartedEvent`
 * :class:`Symfony\\Component\\Messenger\\Event\\WorkerStoppedEvent`
 
+.. versionadded:: 7.4
+
+    The ``MessageSentToTransportsEvent`` event was introduced in Symfony 7.4.
+
+.. note::
+
+    The ``MessageSentToTransportsEvent`` event is dispatched **only** after a
+    message was sent to at least one transport. If the message was sent to
+    multiple transports, the event is dispatched only once.
+
 Additional Handler Arguments
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~