Go list implementation for detecting dependencies

[lseppala]

This replaces the go mod graph implementation with an implementation based on go list, which was suggested here.

This is more accurate than go mod graph because:

• it doesn't contain multiple versions of dependencies
• it will contain only dependencies of the specified build target (no testing and tooling dependencies included, for example)

However, this does not capture transitive dependency relationships. In order to capture transitive dependency relationships, we need to run both go list and go mod graph. However, the operating model of the toolkit library currently limits us to one command per snapshot. The toolkit library will need to be updated to allow for more flexibility before we run both commands.

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This work also adds a simple Go project to demonstrate the Action within this repo itself.

Example run of Action: https://github.com/dsp-testing/go-snapshot-action/actions/runs/2374558077

[mrysav]