Enable a more global auto-wiring

config/services.yaml

 services:
+  # default configuration for services in *this* file
+  _defaults:
+    autowire: true      # Automatically injects dependencies in your services.
+    autoconfigure: true # Automatically registers your services as commands, event subscribers, etc.
+
+  # makes classes in src/ available to be used as services
+  # this creates a service per class whose id is the fully-qualified class name
+  App\:
+    resource: '../src/'
+    exclude:
+      - '../src/DependencyInjection/'
+      - '../src/Entity/'
+      - '../src/Kernel.php'
+      - '../src/Tests/'