minor #6935 Use the standard cache and logs dir for the micro kernel example (javiereguiluz)

This PR was submitted for the 3.0 branch but it was merged into the 3.1 branch instead (closes #6935).

Discussion
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Use the standard cache and logs dir for the micro kernel example

This fixes #6868.

Commits
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ca53cb5 Use the standard cache and logs dir for the micro kernel example

Author: xabbuh

configuration/micro_kernel_trait.rst

@@ -195,6 +195,18 @@ to hold the kernel. Now it looks like this::
             // load the annotation routes
             $routes->import(__DIR__.'/../src/App/Controller/', '/', 'annotation');
         }
+
+        // optional, to use the standard Symfony cache directory
+        public function getCacheDir()
+        {
+            return dirname(__DIR__).'/var/cache/'.$this->getEnvironment();
+        }
+
+        // optional, to use the standard Symfony logs directory
+        public function getLogDir()
+        {
+            return dirname(__DIR__).'/var/logs';
+        }
     }
 
 Unlike the previous kernel, this loads an external ``app/config/config.yml`` file,
@@ -294,9 +306,7 @@ this:
     your-project/
     ├─ app/
     |  ├─ AppKernel.php
-    │  ├─ cache/
     │  ├─ config/
-    │  ├─ logs/
     │  └─ Resources
     |     └─ views
     |        ├─ base.html.twig
@@ -306,6 +316,9 @@ this:
     │  └─ App
     |     └─ Controller
     |        └─ MicroController.php
+    ├─ var/
+    |  ├─ cache/
+    │  └─ logs/
     ├─ vendor/
     │  └─ ...
     ├─ web/