Partially implements #572

This adds packages for dependencies to go modules found within the buildinfo section of a binary compiled with the go compiler.

A few things to note:

• This is a flat representation of transitive dependencies. All dependencies directly relate to the go module this is built for. There are no dependency-to-dependency relationships created. This is a limitation of the ecosystem.
• A relationship is crated for all binaries to the stdlib package.

To make this easier I've updated the cataloger test facilities to take not just full packages (which is difficult to craft for large tests) but instead string representations of packages and use that for assertions. This makes tests that are concerned with wiring and less about correctness in depth to have coverage more easily at the cataloger level. The same was done for relationships.