add read sensor query

internal/domains/sensors/repository.go

@@ -50,10 +50,21 @@ func (p *pgxRepo) UpdateSensor(s Sensor) error {
 	return err
 }
 
-const readSensorBySensorID = ``
+const readSensorBySensorID = `select sensor_id, sensor_type, sampling_interval, threshold_above, threshold_below from sensors where sensor_id = $1`
 
 func (p *pgxRepo) ReadSensor(sensorID string) (Sensor, error) {
-	panic("unimplemented")
+	var s Sensor
+	err := p.QueryRow(context.Background(), readSensorBySensorID, sensorID).Scan(
+		&s.SensorID,
+		&s.SensorType,
+		&s.SamplingInterval,
+		&s.ThresholdAbove,
+		&s.ThresholdBelow,
+	)
+	if err != nil {
+		return Sensor{}, ErrSensorNotFound
+	}
+	return s, nil
 }
 
 const readSensorValuesBySensorID = ``