implement TCW, TCG, TCB in SpectralIndice Process

[Florian-Katerndahl]

a simple if-else-check should suffice; add call to another EMB module which allows the creation of tasseled cap rasters.

[Florian-Katerndahl]

GRASS offers a way to calculate the TC-Components. However, all are output at once and with the current approach, the calculations are done three times anyway, just to return a single band. This structure is currently expected by the workflow but neither elegant nor wise regarding resource consumption.

[Florian-Katerndahl]

The process needs single band files as inputs. This would require the explosion of the input file and thus duplicate processing (because it is done later on anyways).

[Florian-Katerndahl]

Creating a different "route" for the creation of Tasseled Cap bands (maybe in the form of a different sub-workflow) and merging the channel later on into the "normal" indice-channel would work.
The process would emit a four-layer-file which would then be split up into three single-layer-files (last band is not needed currently, assuming we're working with grass7:i.tasscap) and some channel-shenanigans (duplicating some elements of channel entries -> metadata).