Skip ready functions if not in main thread or plugins are not loaded yet (#5005)

* Skip ready functions if not in main thread or plugins are not loaded yet

* Debug integration tests

* Update ready.py

* Update ready.py

* Fix isInMainThread and isPluginRegistryLoaded ready functions

* Preload gunicorn app to only invoke the appconfig ready functions once

* debug: test prints for statistics

* Remove debug print

* Test without

* Revert "Test without"

This reverts commit 1bc1872893.

* Second test

* Add checks back to part, label, user model

* Add checks back to inventree, plugin apps

* log server output for debugging

* hopefully I can get the log this time+

* Next test

* Test with --noreload

* Next test

* trigger: ci, because session expired

* block the second ready execution instead of the first

* fix: load order

* Fix test and revert gh actions workflow change

* Added all_apps method to reload machanism

* Changed detect reload mechanism

* Also trigger ready on reload

* Add skipping second reload back for testing mode

* Added doc string back

* Update InvenTree/plugin/base/integration/AppMixin.py

docker/gunicorn.conf.py

@@ -37,3 +37,6 @@ logger.info(f"Starting gunicorn server with {workers} workers")
 
 max_requests = 1000
 max_requests_jitter = 50
+
+# preload app so that the ready functions are only executed once
+preload_app = True