minor #6109 add link to Monolog configuration (snoek09)

This PR was squashed before being merged into the 2.3 branch (closes #6109).

Discussion
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add link to Monolog configuration

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | #2862

Commits
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9fe931e add link to Monolog configuration

Author: xabbuh

reference/configuration/monolog.rst

@@ -4,6 +4,9 @@
 MonologBundle Configuration ("monolog")
 =======================================
 
+For a full list of handler types and related configuration
+options, see `Monolog Configuration`_.
+
 Full Default Configuration
 --------------------------
 
@@ -101,3 +104,5 @@ Full Default Configuration
     When the profiler is enabled, a handler is added to store the logs'
     messages in the profiler. The profiler uses the name "debug" so it
     is reserved and cannot be used in the configuration.
+
+.. _`Monolog Configuration`: https://github.com/symfony/monolog-bundle/blob/master/DependencyInjection/Configuration.php