feat: configurable window on scheduled notify_credentials jobs

`notify_credentials` has 2 ways of running.
1. The manual,  one-off method  which uses `--args_from_database`  to specify what should be sent.
2. [The automated method](https://github.com/openedx/edx-platform/blob/7316111b35c8db0b93665e00aa4071685d772ab3/openedx/core/djangoapps/credentials/management/commands/notify_credentials.py#L157-L159), which runs on a regular schedule, to catch anything which fell through the cracks.

The automated method does a certain amount of time/date math in order to calculate the entry point of the window based on the current runtime.  This is, I assume, why it has some hardcoded logic; it's not at all simple to have a `cron`-run  management command running on a regular cadence that can do the same time logic.

```py
        if options['auto']:
            options['end_date'] = datetime.now().replace(minute=0, second=0, microsecond=0)
            options['start_date'] = options['end_date'] - timedelta(hours=4)
```

However, it is not ideal that the actual time window of 4 hours is hardcoded directly into `edx-platform`.

This fix

* creates an overridable `NOTIFY_CREDENTIALS_FREQUENCY` that defaults to 14400 seconds (4 hours).
* pulls that frequency into the quoted code

Using seconds allows maximum flexibility.

FIXES: APER-3383

Author: deborahgu

cms/envs/common.py

@@ -2520,6 +2520,8 @@
 CREDENTIALS_INTERNAL_SERVICE_URL = 'http://localhost:8005'
 CREDENTIALS_PUBLIC_SERVICE_URL = 'http://localhost:8005'
 CREDENTIALS_SERVICE_USERNAME = 'credentials_service_user'
+# time between scheduled runs, in seconds
+NOTIFY_CREDENTIALS_FREQUENCY = 14400
 
 ANALYTICS_DASHBOARD_URL = 'http://localhost:18110/courses'
 ANALYTICS_DASHBOARD_NAME = 'Your Platform Name Here Insights'

lms/envs/common.py

@@ -4331,6 +4331,8 @@ def _make_locale_paths(settings):  # pylint: disable=missing-function-docstring
 
 CREDENTIALS_INTERNAL_SERVICE_URL = 'http://localhost:8005'
 CREDENTIALS_PUBLIC_SERVICE_URL = 'http://localhost:8005'
+# time between scheduled runs, in seconds
+NOTIFY_CREDENTIALS_FREQUENCY = 14400
 
 COMMENTS_SERVICE_URL = 'http://localhost:18080'
 COMMENTS_SERVICE_KEY = 'password'

openedx/core/djangoapps/credentials/management/commands/notify_credentials.py

@@ -13,6 +13,7 @@
 
 from datetime import datetime, timedelta
 import dateutil.parser
+from django.conf import settings
 from django.core.management.base import BaseCommand, CommandError
 from opaque_keys import InvalidKeyError
 from opaque_keys.edx.keys import CourseKey
@@ -157,8 +158,9 @@ def handle(self, *args, **options):
             options = self.get_args_from_database()
 
         if options["auto"]:
+            run_frequency = settings.NOTIFY_CREDENTIALS_FREQUENCY
             options["end_date"] = datetime.now().replace(minute=0, second=0, microsecond=0)
-            options["start_date"] = options["end_date"] - timedelta(hours=4)
+            options["start_date"] = options["end_date"] - timedelta(seconds=run_frequency)
 
         log.info(
             f"notify_credentials starting, dry-run={options['dry_run']}, site={options['site']}, "

openedx/core/djangoapps/credentials/management/commands/tests/test_notify_credentials.py

@@ -7,7 +7,7 @@
 
 from django.core.management import call_command
 from django.core.management.base import CommandError
-from django.test import TestCase, override_settings  # lint-amnesty, pylint: disable=unused-import
+from django.test import TestCase, override_settings
 from freezegun import freeze_time
 
 from openedx.core.djangoapps.catalog.tests.factories import ProgramFactory, CourseFactory, CourseRunFactory
@@ -125,6 +125,7 @@ def test_multiple_programs_uuid_args(self, mock_get_programs, mock_task):
 
     @freeze_time(datetime(2017, 5, 1, 4))
     def test_auto_execution(self, mock_task):
+        """Verify that an automatic execution designed for scheduled windows works correctly"""
         self.expected_options['auto'] = True
         self.expected_options['start_date'] = datetime(2017, 5, 1, 0, 0)
         self.expected_options['end_date'] = datetime(2017, 5, 1, 4, 0)
@@ -133,6 +134,20 @@ def test_auto_execution(self, mock_task):
         assert mock_task.called
         assert mock_task.call_args[0][0] == self.expected_options
 
+
+    @override_settings(NOTIFY_CREDENTIALS_FREQUENCY=3600)
+    @freeze_time(datetime(2017, 5, 1, 4))
+    def test_auto_execution_different_schedule(self, mock_task):
+        """Verify that an automatic execution designed for scheduled windows
+        works correctly if the window frequency has been changed"""
+        self.expected_options["auto"] = True
+        self.expected_options["start_date"] = datetime(2017, 5, 1, 3, 0)
+        self.expected_options["end_date"] = datetime(2017, 5, 1, 4, 0)
+
+        call_command(Command(), "--auto")
+        assert mock_task.called
+        assert mock_task.call_args[0][0] == self.expected_options
+
     def test_date_args(self, mock_task):
         self.expected_options['start_date'] = datetime(2017, 1, 31, 0, 0, tzinfo=timezone.utc)
         call_command(Command(), '--start-date', '2017-01-31')