Add codecov (#6967)

* add codecov upload

* add to readme

* add flags

* dummy change

* dummy change

* switch to inventree org

* add codecov yaml

* lower threshold (for now)
see https://github.com/inventree/InvenTree/pull/6945 for a possibility to get it up again

src/backend/InvenTree/InvenTree/urls.py

@@ -385,6 +385,7 @@ if settings.ENABLE_CLASSIC_FRONTEND:
 
 classic_frontendpatterns = [
     # Apps
+    #
     path('build/', include(build_urls)),
     path('common/', include(common_urls)),
     path('company/', include(company_urls)),