Vendor the githubrelease module

[justinmayer]

The current shipped githubrelease package on PyPI is lacking a fix for a problem affecting the use of implicitly-populated GITHUB_TOKEN environment variables. To be clear, the problem is already fixed via scikit-build/github-release#73 but isn't yet available in a shipped release on PyPI.

Moreover, there is a problem with that project's setup.py configuration that prevents installing directly from the githubrelease repository's master branch. Related PR: scikit-build/github-release#76

After thinking of the many hours I have spent dealing with this issue as well as other problems related to githubrelease, I am currently of the mind that we should vendor this module inside AutoPub. That would give us agency and direct control over its behavior, without having to be reliant on the upstream project.

Related discussion:

• Use forked githubrelease as temporary CI fix pelican-plugins/photos#112
• Switch to using the repository token for release creation pelican-plugins/photos#99 (comment)