add git-buildpackage/lintian job with .deb artifact

This is based on my work to make a standard gitlab CI image for any package based on git-buildpackage. The goal is ultimately to make this the standard gitlab CI image for salsa.debian.org. It currently automatically installs Build-Depends, runs gbp buildpackage -uc -us then runs lintian. Soon it will also auto-detect packages set up for autopkgtest and run them.