Add CI workflow to check for unapproved Go dependency licenses

[per1234]

A task and GitHub Actions workflow are provided here for checking the license types of Go project dependencies.

On every push and pull request that affects relevant files, the CI workflow will use Licensed to check:

• If the dependency licenses cache is up to date
• If any of the project's dependencies have an unapproved license type.

Approval can be based on:

• Allowed license type
• Individual dependency