Publish pressure-vessel releases, separate from scout releases

• build-relocatable-install: Separate copyright files for util-linux

  Unusually, libblkid1 and libmount1 have different copyright files despite being from the same package. Ship both.

• CI: Make relocatable builds with both production and debug binaries

  The production build uses dpkg packages, built with -O2 -g and stripped. This is similar to what we currently extract from a scout SDK build; but if we do it here, we can decouple the pressure-vessel release process from the scout release process, making it possible to issue a new pressure-vessel release for use with pre-existing scout/soldier runtimes much quicker than the time needed to do an entire scout release.

• CI: Add infrastructure to upload pressure-vessel releases

  When combined with changes to SteamLinuxRuntime scripts, this will let us do a new pressure-vessel release and incorporate it into soldier/sniper/etc. depots, without having to do a whole release of scout to provide the new pressure-vessel.

  These releases don't include anything that we didn't already publish in Gitlab artifacts, and they're relatively small, so they might as well be public immediately (unlike the full scout releases, which we avoid publishing before they are final, both because they are rather large and because game developers could get compatibility issues if they build against a non-finalized scout runtime).