Reduce CI-built docker image size

[marip8]

The tesseract docker image that is produced in CI is fairly large (~5 Gb), a good chunk of which is the artifacts of the build that are not deleted (600Mb for tesseract). This PR adds a final step to the CI to remove the build directories of the target and upstream workspaces to reduce the size of the saved docker image

[marip8]

I think we could probably also uninstall all -dev libraries as well before the test stage to further reduce. Playing around with the docker image manually showed that reduced the size of the /usr directory from ~3.3Gb to ~2.2Gb

[Levi-Armstrong]

Can't you also remove the source?

[marip8]

We could remove the source too, but it's only ~180Mb (I think due to a clone depth of 1), so I didn't think it was worth it. I can add it if you want though

[Levi-Armstrong]

We could remove the source too, but it's only ~180Mb (I think due to a clone depth of 1), so I didn't think it was worth it. I can add it if you want though

Nah, just thinking of other things that may be able to reduce it.

What about the following commands? These are commonly used when generating dockers, but never looked into how much space they save.

apt-get clean && rm -rf /var/lib/apt/lists/*

[marip8]

What about the following commands?

Turns out its only 45Mb in this particular image, so I'm not sure it's worth adding in the interest of keeping the AFTER_SCRIPT short