Worker thread fix (#6733) (#6735)

* Do not enforce INVENTREE_LOG_LEVEL in dockerfile

- Already defaults to WARNING anyway
- Prevents override in config file

* Enable plugin loading in worker thread

(cherry picked from commit c82713328d)

Co-authored-by: Oliver <oliver.henry.walters@gmail.com>

Dockerfile

@@ -23,7 +23,6 @@ ENV PYTHONUNBUFFERED 1
 ENV PIP_DISABLE_PIP_VERSION_CHECK 1
 ENV INVOKE_RUN_SHELL="/bin/ash"
 
-ENV INVENTREE_LOG_LEVEL="WARNING"
 ENV INVENTREE_DOCKER="true"
 
 # InvenTree paths

InvenTree/plugin/apps.py

@@ -10,7 +10,7 @@ from django.apps import AppConfig
 
 from maintenance_mode.core import set_maintenance_mode
 
-from InvenTree.ready import canAppAccessDatabase, isInMainThread
+from InvenTree.ready import canAppAccessDatabase, isInMainThread, isInWorkerThread
 from plugin import registry
 
 logger = logging.getLogger('inventree')
@@ -24,7 +24,8 @@ class PluginAppConfig(AppConfig):
     def ready(self):
         """The ready method is extended to initialize plugins."""
         # skip loading if we run in a background thread
-        if not isInMainThread():
+
+        if not isInMainThread() and not isInWorkerThread():
             return
 
         if not canAppAccessDatabase(