Adds retry logic for ss.

1. Created a new celery queue with key `SOFTWARE_SECURE_VERIFICATION_ROUTING_KEY`.
2. Added a celery task with retry logic.
3. sorted imports with isort.
4. Changed deprecated `log.warn` => `log.warning`.

openedx/tests/settings.py

@@ -122,3 +122,9 @@ RETIREMENT_SERVICE_WORKER_USERNAME = 'RETIREMENT_SERVICE_USER'
 RETIRED_USERNAME_PREFIX = 'retired__user_'
 
 PROCTORING_SETTINGS = {}
+
+# Software Secure request retry settings
+# Time in seconds before a retry of the task should be 60 mints.
+SOFTWARE_SECURE_REQUEST_RETRY_DELAY = 60 * 60
+# Maximum of 6 retries before giving up.
+SOFTWARE_SECURE_RETRY_MAX_ATTEMPTS = 6