Mx-C: Edge caching headers on public utility endpoints

Add Cache-Control: public, max-age=3600, stale-while-revalidate=86400 on /api/v1/utilities, /api/v1/utilities/{slug}, /api/v1/utilities/by-eia-id/{id}, /api/v1/territories/{id}.geojson. Makes DataLoader-batched fan-out from CRM cheap at steady-state.