Cache service data retention in Redis

Adds caching for service data retention. This removes separate API
client methods to retrieve individual data retention records by id
or type in favor of a single method that fetches and caches all
retention settings configured for the service. This makes it much
easier to invalidate cache when settings change.

Lookup by id or type is provided by helper methods in the service
model.

tests/app/main/views/test_send.py

@@ -2002,7 +2002,7 @@ def test_create_job_should_call_api(
     mock_get_job,
     mock_get_notifications,
     mock_get_service_template,
-    mock_get_service_data_retention_by_notification_type,
+    mock_get_service_data_retention,
     mocker,
     fake_uuid,
     when