Update Earth-Sun distance computation

OTB compute the earth sun distance based on formula extracted from 6S in file otbVarSol.h. A more accurate value can be computed based on planetary ephemeris files. This computation can be provided based on the CALCEPH open source tool.

The goal of this feature is to provide the possibility to set externally this value in the Optical Calibration app and in the related filters. If the value is not set, the filter uses the current formula.

A python script based on calceph python wrapping can be provided to compute the distance externally.