[FR] [Plugin] Check if all plugins are really installed

Fixes #2524

InvenTree/plugin/apps.py

@@ -30,6 +30,7 @@ class PluginAppConfig(AppConfig):
 
                 if not registry.is_loading:
                     # this is the first startup
+                    registry.check_plugin_file()
                     registry.collect_plugins()
                     registry.load_plugins()