Page settings: toggle visibility of incident/maintenance history sections

[cl8dep]

Context

Part of the pages builder (#15). When a page can be configured via settingsJson, the admin should be able to enable/disable the incident history and maintenance history sections per page.

What to implement

• Add showIncidentHistory: bool and showMaintenanceHistory: bool to Page.settingsJson schema
• Admin page editor (Pages builder: multi-page, service ordering, page settings #15) should expose these toggles
• Public /incidents history page reads these flags from the page config and returns 404 if both are disabled
• Currently (before Pages builder: multi-page, service ordering, page settings #15 ships) the history page is always visible — this issue adds the conditional logic

Depends on

• Pages builder: multi-page, service ordering, page settings #15 (Pages builder: multi-page, page settings)