[Doc] Workflow 3d gw model from dgm (#2438)

...flows/Example-of-a-DGM-to-model-workflow/01_load-tifs.png

...lows/Example-of-a-DGM-to-model-workflow/02_merge-DEMs.png

...of-a-DGM-to-model-workflow/03_create-shp-for-clipping.png

...e-of-a-DGM-to-model-workflow/04_edit-save-new-polygon.png

.../workflows/Example-of-a-DGM-to-model-workflow/05_clip.png

...xample-of-a-DGM-to-model-workflow/06_reproject-raster.png

...of-a-DGM-to-model-workflow/07_reproject-vector-layers.png

...xample-of-a-DGM-to-model-workflow/08_vector-to-raster.png

...f-a-DGM-to-model-workflow/09_bathymetry-depth-to-elev.png

...kflows/Example-of-a-DGM-to-model-workflow/10_save-asc.png

...e-of-a-DGM-to-model-workflow/11_contour-for-coastline.png

...xample-of-a-DGM-to-model-workflow/12_select-non-coast.png

...xample-of-a-DGM-to-model-workflow/13_remove-non-coast.png

.../Example-of-a-DGM-to-model-workflow/14_simplify-coast.png

...-DGM-to-model-workflow/15_delete-unnecessary-vertices.png

...xample-of-a-DGM-to-model-workflow/16_polygone-to-line.png

...ample-of-a-DGM-to-model-workflow/17_remove-all-fields.png

...ple-of-a-DGM-to-model-workflow/18_merge-vector-layers.png

...lows/Example-of-a-DGM-to-model-workflow/19a_save-gmsh.png

...Example-of-a-DGM-to-model-workflow/19b_create-2d-mesh.png