Add reflected_irradiance to measurement_type_id in order to capture downfacing pyranometer measurement

[BiancaMorandi]

As for definition given here: https://www.hukseflux.com/products/pyranometers-solar-radiation-sensors/albedometers, the "albedometers are instruments that measure global and reflected solar radiation, and the solar albedo. An albedometer is composed of two pyranometers; the upfacing one measuring global solar radiation, the downfacing one measuring reflected solar radiation. Albedo is defined as the ratio of the reflected to the global radiation."

Often the measurements recorded by an albedo sensor are only global and reflected solar radiation and sometimes albedo might be also calculated by the sensor. The reflected_irradiance measurement type is not included yet in the measurement_type_id list. I am suggesting to add this in order to be able to correctly identify the measurement type measured by the downfacing pyranometer constituting the albedometer.