Homogenize generator description (generated with kicad-footprint-generator xxx) for all generators

Centralized adding the string generated with kicad-footprint-generator '{generator_name}' to the description.

With this MR all footprints (without exception) get the same string with {generator_name} matching the exact name of the generator.

In case we want to change the string to something else, it would be good to do that now, i.e. before merging this.