Resolve "Implement Lambda: count_emergency_vehicles"

Tested after db setup via setup_db lambda and the following event

{
"1704071400": "images/street_5/camera_1/2023-12-19_01-29.png",
"1704062000": "images/street_5/camera_1/2023-12-19_01-30.png",
"1704062600": "images/street_5/camera_1/2023-12-19_01-31.png"
}