racecar_analytics update structs for db mapping

model.go

type ECU struct {
	ID            int       `json:"id" gorm:"primaryKey"`		// add this
	MotorRPM      int       `json:"motor_rpm"`
	Speed         int       `json:"speed"`
	Throttle      int       `json:"throttle"`
	BrakePressure int       `json:"brake_pressure"`
	CreatedAt     time.Time `json:"created_at" gorm:"precision:6"`	// add this
}

type Battery struct {
	ID           int       `json:"id" gorm:"primaryKey"`		// add this
	ChargeLevel  int       `json:"charge_level"`
	CellTemp1    int       `json:"cell_temp_1"`
	CellTemp2    int       `json:"cell_temp_2"`
	CellTemp3    int       `json:"cell_temp_3"`
	CellTemp4    int       `json:"cell_temp_4"`
	CellVoltage1 int       `json:"cell_voltage_1"`
	CellVoltage2 int       `json:"cell_voltage_2"`
	CellVoltage3 int       `json:"cell_voltage_3"`
	CellVoltage4 int       `json:"cell_voltage_4"`
	CreatedAt    time.Time `json:"created_at" gorm:"precision:6"`	// add this
}