minor #18901 [Monolog] Improve how processors are applied to single channels (javiereguiluz)

This PR was squashed before being merged into the 5.4 branch.

Discussion
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[Monolog] Improve how processors are applied to single channels

Fixes #18217.

Commits
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d390ee3 [Monolog] Improve how processors are applied to single channels

Author: javiereguiluz

logging/processors.rst

@@ -270,8 +270,8 @@ the ``monolog.processor`` tag:
 Registering Processors per Channel
 ----------------------------------
 
-You can register a processor per channel using the ``channel`` option of
-the ``monolog.processor`` tag:
+By default, processors are applied to all channels. Add the ``channel`` option
+to the ``monolog.processor`` tag to only apply a processor for the given channel:
 
 .. configuration-block::
 
@@ -281,7 +281,7 @@ the ``monolog.processor`` tag:
         services:
             App\Logger\SessionRequestProcessor:
                 tags:
-                    - { name: monolog.processor, channel: main }
+                    - { name: monolog.processor, channel: 'app' }
 
     .. code-block:: xml
 
@@ -297,7 +297,7 @@ the ``monolog.processor`` tag:
 
             <services>
                 <service id="App\Logger\SessionRequestProcessor">
-                    <tag name="monolog.processor" channel="main"/>
+                    <tag name="monolog.processor" channel="app"/>
                 </service>
             </services>
         </container>
@@ -309,7 +309,7 @@ the ``monolog.processor`` tag:
         // ...
         $container
             ->register(SessionRequestProcessor::class)
-            ->addTag('monolog.processor', ['channel' => 'main']);
+            ->addTag('monolog.processor', ['channel' => 'app']);
 
 .. _`Monolog`: https://github.com/Seldaek/monolog
 .. _`built-in Monolog processors`: https://github.com/Seldaek/monolog/tree/main/src/Monolog/Processor