Collection: Users
Document ID: userId (from Firebase Authentication)
Fields - email, username, avatar, active (boolean), bikeId (can be null or an id), history (an array of parkingSpotIds)
Collection: Bikes
Document ID: bikeId
Fields - userId, details (could be an object with bike details), parkedSpotId
Collection: ParkingSpots
Document ID - parkingSpotId
Fields - details (object with parking spot details), ratings (array of objects with userId and rating), comments (array of objects with userId and comment)