Implement extra_test_depends config option for packages entries
Add an extra_test_deps to top level of debcargo.toml where autopkgtest dependencies can be added. A first simple implementation of this feature for https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=949959
Might be extended later by adding the same field to the [packages.lib*] entries if dependencies are required by some tests only, but must not be present on others.
Edited by Wolfgang Silbermayr