Integrate source interface + landing page scan results in directory

[eloquence]

This is an epic to work towards an integration of source interface and landing page scan results in the SecureDrop directory as described here. Details of the epic will evolve as this discussion continues, and we will add tasks below as appropriate.

Lower priority improvements to scan results that can be completed after the launch of the initial integration are not part of this epic. These types of landing page page scanner improvements are tracked through this label.

Phase 1: Core feature set for landing page scans

Preparatory:

• Finalize icon set for directory badges - [scanner integration] Finalize icon set for directory badges #489
• Check the plan below against a threat model for landing pages - [scanner integration] Check integration plan against a threat model for landing pages #512
• Enable the landing page scanner and collect baseline scan data - [scanner integration] Enable landing page scanner and collect baseline scan data #518

Delisting logic:

• Support "delisted" state for individual directory entries - [scanner integration] Support "delisted" state for directory entries #491
• Automatically delist instances with major landing page HTTPS issues - [scanner integration] Automatically delist instances with major landing page HTTPS issues #492
• Automatically delist instances with landing pages served with non-200 HTTP status - [scanner integration] Automatically delist instances with landing pages served with non-200 HTTP status #493

Pre-launch scanner improvements:

• Support landing page redirects on the same domain - [scanner integration] Support landing page redirects on the same domain #494
• Check for assets on third party domain - Check landing pages for assets on third party domain #506 (may choose to defer)
• Add support for Referrer-Policy header - [scanner integration] Add support for Referrer-Policy header #515

Warning logic:

• Add support for "moderate" and "severe" warnings on directory entry pages - [scanner integration] Add support for "moderate" and "severe" warnings on directory entry pages #514
• Create per-request flag for showing warnings about landing page issues - [scanner integration] Create per-request flag for showing landing page warnings #498
• Show severe warning on directory entry page for entries with third party assets or analytics scripts - [scanner integration] Show severe warning on directory entry page for entries with third party assets/analytics scripts #496
• Show moderate warning on directory entry page for landing pages hosted on subdomain - [scanner integration] Show moderate warning on directory entry page for landing pages hosted on subdomain #497
• Show moderate warning on directory entry page for landing pages without Referrer Policy - [scanner integration] Show moderate warning on directory entry page for landing pages with incorrect Referrer Policy #516
• Show moderate warning on directory entry page for landing pages with links to .onion addresses - [scanner integration] Show moderate warning on directory entry page for landing pages with links to .onion addresses #517

Deployment:

• Give news organizations time to address landing page issues - [scanner integration] Give news organizations time to address landing page issues #499
• Make warning display the default - [scanner integration] Make warning display the default #500

Phase 2: Source interface support

• Associate source interface scan results with directory entries - [scanner integration] Associate source interface scan results with directory entries #501
• Display SecureDrop version on directory entry - [scanner integration] Display SecureDrop version on directory entry #502
• Display "Unreachable" icon and SecureDrop downtime - [scanner integration] Display "Unreachable" icon and SecureDrop downtime #503
• Automatically delist instances with extended downtime - [scanner integration] Automatically delist instances with extended downtime #504