Add symfony/config as a dependency

Fixes this error:

> Error: Class
> 'Symfony\Component\Config\Resource\ClassExistenceResource' not found
> in
> Symfony\Component\DependencyInjection\Compiler\AutowirePass->createTypeNotFoundMessage()

composer.json

@@ -20,7 +20,8 @@
         "drupal/core-composer-scaffold": "^9.0",
         "drupal/core-recommended": "^9.0",
         "drupal/upgrade_status": "^2.9",
-        "drush/drush": "^10.3"
+        "drush/drush": "^10.3",
+        "symfony/config": "^4"
     },
     "require-dev": {
         "drupal/core-dev": "^9.0"

composer.lock

@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "9eb002bfeb9df152d41a7b8f4bcb41fa",
+    "content-hash": "e76f842adfa02653c889e81703a1aeef",
     "packages": [
         {
             "name": "asm89/stack-cors",
@@ -3916,6 +3916,84 @@
             ],
             "time": "2020-05-27T08:26:50+00:00"
         },
+        {
+            "name": "symfony/config",
+            "version": "v4.4.13",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/symfony/config.git",
+                "reference": "043bf8652c307ebc23ce44047d215eec889d8850"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/symfony/config/zipball/043bf8652c307ebc23ce44047d215eec889d8850",
+                "reference": "043bf8652c307ebc23ce44047d215eec889d8850",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=7.1.3",
+                "symfony/filesystem": "^3.4|^4.0|^5.0",
+                "symfony/polyfill-ctype": "~1.8"
+            },
+            "conflict": {
+                "symfony/finder": "<3.4"
+            },
+            "require-dev": {
+                "symfony/event-dispatcher": "^3.4|^4.0|^5.0",
+                "symfony/finder": "^3.4|^4.0|^5.0",
+                "symfony/messenger": "^4.1|^5.0",
+                "symfony/service-contracts": "^1.1|^2",
+                "symfony/yaml": "^3.4|^4.0|^5.0"
+            },
+            "suggest": {
+                "symfony/yaml": "To use the yaml reference dumper"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "4.4-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Symfony\\Component\\Config\\": ""
+                },
+                "exclude-from-classmap": [
+                    "/Tests/"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Fabien Potencier",
+                    "email": "fabien@symfony.com"
+                },
+                {
+                    "name": "Symfony Community",
+                    "homepage": "https://symfony.com/contributors"
+                }
+            ],
+            "description": "Symfony Config Component",
+            "homepage": "https://symfony.com",
+            "funding": [
+                {
+                    "url": "https://symfony.com/sponsor",
+                    "type": "custom"
+                },
+                {
+                    "url": "https://github.com/fabpot",
+                    "type": "github"
+                },
+                {
+                    "url": "https://tidelift.com/funding/github/packagist/symfony/symfony",
+                    "type": "tidelift"
+                }
+            ],
+            "time": "2020-08-10T07:27:51+00:00"
+        },
         {
             "name": "symfony/console",
             "version": "v4.4.9",