[Configuration] Add documentation about ignore_errors: not_found option.

Author: pulzarraider

configuration.rst

@@ -88,8 +88,10 @@ configuration files, even if they use a different format:
         # config/services.yaml
         imports:
             - { resource: 'legacy_config.php' }
-            # ignore_errors silently discards errors if the loaded file doesn't exist
-            - { resource: 'my_config_file.xml', ignore_errors: true }
+            # ignore_errors: not_found silently discards errors if the loaded file doesn't exist
+            - { resource: 'my_config_file.xml', ignore_errors: not_found }
+            # ignore_errors: true silently discards errors if the loaded file doesn't exist or contains invalid code
+            - { resource: 'my_other_config_file.xml', ignore_errors: true }
             # glob expressions are also supported to load multiple files
             - { resource: '/etc/myapp/*.yaml' }
 
@@ -108,8 +110,10 @@ configuration files, even if they use a different format:
 
             <imports>
                 <import resource="legacy_config.php"/>
-                <!-- ignore_errors silently discards errors if the loaded file doesn't exist -->
-                <import resource="my_config_file.yaml" ignore-errors="true"/>
+                <!-- ignore-errors="not_found" silently discards errors if the loaded file doesn't exist -->
+                <import resource="my_config_file.yaml" ignore-errors="not_found"/>
+                <!-- ignore-errors="true" silently discards errors if the loaded file doesn't exist or contains invalid code -->
+                <import resource="my_other_config_file.yaml" ignore-errors="true"/>
                 <!-- glob expressions are also supported to load multiple files -->
                 <import resource="/etc/myapp/*.yaml"/>
             </imports>
@@ -121,14 +125,20 @@ configuration files, even if they use a different format:
 
         // config/services.php
         $loader->import('legacy_config.xml');
-        // the third optional argument of import() is 'ignore_errors', which
-        // silently discards errors if the loaded file doesn't exist
+        // the third optional argument of import() is 'ignore_errors'
+        // 'ignore_errors' set to 'not_found' silently discards errors if the loaded file doesn't exist
+        $loader->import('my_config_file.yaml', null, 'not_found');
+        // 'ignore_errors' set to true silently discards errors if the loaded file doesn't exist or contains invalid code
         $loader->import('my_config_file.yaml', null, true);
         // glob expressions are also supported to load multiple files
         $loader->import('/etc/myapp/*.yaml');
 
         // ...
 
+.. versionadded:: 4.4
+
+    The ``not_found`` option value for ``ignore_errors`` was introduced in Symfony 4.4.
+
 .. _config-parameter-intro:
 .. _config-parameters-yml:
 .. _configuration-parameters:
@@ -797,7 +807,7 @@ parameters at once by type-hinting any of its constructor arguments with the
 
     // src/Service/MessageGenerator.php
     namespace App\Service;
-    
+
     // ...
 
     use Symfony\Component\DependencyInjection\ParameterBag\ContainerBagInterface;