Use AOT value from L1B metadata file as default value for AC.
Currently, SICOR uses a default AOT value of 0.2 fixed in the options file for the AC. However, the L1B metadata contain a "sceneAOT" entry providing an AOT value probably estimated by the AC from DLR. Instead of an arbitrary AOT we could use this value for SICOR by adding it as an attribute to the EnMAP L1B object. Although we will implement an own AOT retrieval next year, it would be good to have an accurate default value available as fallback. @danschef What do you think?