Fixes #14692 - set default variables for sidebar totals

[snipe]

This one slipped past me . The AssetCountForSidebar middleware does some quick counting queries and shares with them all views for easy access and totals in the sidebar. Unfortunately, since this middleware also fires during /setup, where the migrations might not have been run yet, you might run into a 500 error on setup (since we're querying tables that might not exist until the next screen (which is database migrations).

Fixes #14692

[what-the-diff]

PR Summary

• New Variables Introduction
  This update adds four pivotal variables into the system – total_due_for_checkin, total_overdue_for_checkin, total_due_for_audit and total_overdue_for_audit. By implementing these variables, it becomes simpler to monitor and manage assignments and audits. It ensures that tasks or audits that are due or past their due dates don't slip through the cracks. The addition of these variables sets the stage for better productivity and efficiency, enabling the system to keep a much tighter grip on timelines.