Implement post-job actions in GFMAP (Rasterization purpose)

[GriffinBabe]

Implement a way of triggering post-job actions in GFMAP. Once a openeo job is finished, its content is downloaded and the job task is performed locally based on the newly downloaded file.

@kvantricht This task is directly related to the generation of label rasters (rasterization process). For example, we can link this post-job with the extraction of sentinel-2 data

[GriffinBabe]

Implemented and about to be merged #45