[Prod] Add training report dashboard, and the backend for the statistics widget

[thewatermethod]

Description of change

• Add "training_report_dashboard" feature flag
• For a user that doesn't have the flag/is not an admin, nothing will change
• For a user with the flag, or as an admin, the regional dashboard now has tabs at the top. I've left the vestigial "/" path there despite it not correlating to a tab link, so going to the base page means you will see tabs without an active link
• Setup routes at "/training-reports" and "/all-reports." These are empty dashboard pages.
• A backend only change for the TR dashboard overview widget.

How to test

• Confirm that for a user without flag/admin privileges, the experience on the regional dashboard is unchanged.
• Confirm that for an admin/flagged user, that the tab navigation appears on /regional-dashboard and that the two links take you to empty dashboard pages

Issue(s)

• https://jira.acf.gov/browse/TTAHUB-2507
• https://jira.acf.gov/browse/TTAHUB-2754

Checklists

Every PR

• Meets issue criteria
• JIRA ticket status updated
• Code is meaningfully tested
• Meets accessibility standards (WCAG 2.1 Levels A, AA)
• API Documentation updated
• Boundary diagram updated
• Logical Data Model updated
• Architectural Decision Records written for major infrastructure decisions
• UI review complete

Before merge to main

• OHS demo complete
• Ready to create production PR

Production Deploy

• Staging smoke test completed

After merge/deploy

• Update JIRA ticket status