Add GTKWave to at least one image

[umarcor]

Currently, GTKWave is built and a package image is generated, but it is not used in any of the other images. In fact, it is used in ghdl/docker (https://github.com/ghdl/docker/blob/master/gui.dockerfile#L29-L34), but not here.

We should, at least, generate an image containing GTKWave alone. Optionally, we might add it on top of sim or formal images.

/cc @tmeissner

[umarcor]

FTR, an standalone gtkwave image is provided already (see 95dfe3f). This issue is kept open to track adding gtkwave to other images.