[Feature] Add repositories to Go dependencies

## Context
The Go dependency tree generator does not return the repositories of dependencies.

The `repository` field [here](https://github.com/canonical/source-wand/blob/c5624631ece6cd8fc405c13289ee8a6e45a11516/dependency-analysis/src/dependency_tree_generators/go_dependency_tree_generator.rs#L86) is an empty string.

## What should be done
Go dependencies are git URLs already so the dependency tree generator should just return that repository URL.

Start in dependency-analysis/src/dependency_tree_generators/go_dependency_tree_generator.rs at the repository field noted in the issue. Read how Go dependency URLs are represented and how the dependency tree is assembled; done means the generated dependency entries return their existing git repository URLs instead of empty strings.

Written by the indexing model from the issue text.