Trusted Publishing for MFA-level security while using CI to push

[indirect]

• Discuss and design the simplest possible UX for publishing gems from GitHub
• Implement a streamlined web UI for gem authors publishing from GitHub, with no more than 3 required form fields, a la https://docs.pypi.org/trusted-publishers/adding-a-publisher/
• Implement a GitHub action for pushing a gem that requires only one step, with zero arguments, a la https://docs.pypi.org/trusted-publishers/using-a-publisher/ new or updated GitHub action for push (aka one-line trusted publishing) #4286
• Write guide documentation, walking a hypothetical user with a gem hosted on GitHub through each step (with screenshots), showing them how to publish their existing gem automatically via GitHub actions using a short-lived OIDC token
• Address trusted publishing feedback from soft launch testers Address trusted publishing feedback #4283
• Write a blog post about trusted publishing and how it's great and everyone should use it blog post about trusted publishing rubygems.github.io#172
• Celebrate that Trusted Publishing has publicly launched! 🎉