Speckle Spatial filtering processing

Implement spatial speckle filtering with OTBDespeckle application.

Provide an optional spatial despeckling after concatenation.

Typical option evolution

[Filtering]
filter_type = None/Lee/Frost/Gammamap/Kuan
keep_non_filtered_data = True/False
rad     = ... # for all
nblooks = ... # for lee, gammamap & kuan
deramp  = ... # for frost

In case no masking is done and the calibrated image isn't required (need an option), this extra processing could be chained in memory.