Introduce multi-stage build, actually build our code

[SequeI]

No description provided.

[bkabrda]

Let's do the same in Dockerfile.tuffer as well.

[bkabrda]

I also found out that this produces an image with size ~16 GB. The problem is in keeping the whole target/ directory (14 GB) produced by cargo build - it should be safe to remove it after the build to save up space.

Edit: prior to that, target/release/tuftool has to be copied to /usr/bin/ to actually be usable.
Edit 2: one more nit - it might be good to copy into a new directory in e.g. /tmp. Right now the files get copied to container root, which could pollute things in an unexpected way.

[fghanmi]

LGTM!

[openshift-ci]

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