add FRET tool back to Docker image and document its use

[kiniry]

It would be nice if we could ship a working version of FRET and its dependencies in the HARDENS docker image.

We should be able to do so, even if it has X11 dependencies, as we have accomplished such things before in order to run web-page tools from outside of the container through exposed ports. There are prolific nodejs-based images, after all.

[podhrmic]

I was actually looking at FRET yesterday for another project. To your request - we have had more luck with VMs for GUI based tools, so I would be careful with X11 and docker. Also, keep in mind that FRET with out HARDENS requirements is fairly slow running natively with hardware acceleration on my Ubuntu machine, so any non-native solution will likely be even slower (but that is just a limitation of the app).

Perhaps this could be labeled as "Someday"?

[kiniry]

I documented dependencies in the Dockerfile.

[kiniry]

And, indeed, I moved this to Someday.

[podhrmic]

FYI we ran into the same issue (dockerizing FRET) on SpaceBCN - the solution was a dedicated VM. I can link it from HARDENS repo, since it is a simple Ubuntu 20.04 machine with Fret dependencies installed.