Adding code to output pytest warnings. (#22570)

* Added pytest-json-report plugin
	- modifying app-opts in setup.cfg
	- adding hook to all conftest.py files in repo
	- setting report to be saved to test_root/log/warnings.json
	- Writing custom logic to save json report to avoid overwrite if pytest called twice
This was created to allow us to easily parse through test warnings in jenkins

common/test/conftest.py

@@ -3,6 +3,7 @@
 # Patch the xml libs before anything else.
 
 
+from openedx.core.pytest_hooks import pytest_configure  # pylint: disable=unused-import
 from safe_lxml import defuse_xml_libs
 
 defuse_xml_libs()