Improve docker images (versioning, cleanup)

[orzechow]

Some cleanup and preps for

• Setup continuous deployments (releases + ghcr.io docker image)  #59

Based on pacman demo branch, because it also affects the demo docker image

[orzechow]

@ll-nick Could you have a brief look? 🙃

[ll-nick]

Yup, that looks good to me :)

We'll have adjust #61 to copy the tests in the unit test stage (should we use this solution) but I'm guessing that you'll make some adjustments to that one anyway, so feel free to merge.

[orzechow]

We'll have adjust #61 to copy the tests in the unit test stage (should we use this solution) but I'm guessing that you'll make some adjustments to that one anyway, so feel free to merge.

Good point, I added it here, see 68c648d

Btw. with an upcoming dockerfile version, we can shrink that copy command to a single line (and layer):
COPY --parents CMakeLists.txt cmake include test /tmp/arbitration_graphs/
See https://docs.docker.com/reference/dockerfile/#copy---parents