test: Migrate CI to GitHub

[evansims]

Changes

This pull request replaces our current CircleCI continuous integration suite for auth0-react with a new workflow using GitHub Actions.

References

Please see internal ticket SDK-4457.

Testing

This pull request replaces our continuous integration suite with one built in GitHub's native Actions ecosystem. It aligns with other migrations taking place across our repositories.

Checklist

• [x] I have read the Auth0 general contribution guidelines
• [x] I have read the Auth0 Code of Conduct
• [x] All existing and new tests complete without errors
• [x] Rubocop passes on all added/modified files
• [x] All active GitHub checks have passed

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[evansims]

@stevehobbsdev Thanks for your review! I've removed the gem-release dependency and updated the publishing workflow. I think I caught all the related bits and pieces, but let me know if I happened to overlook one.

Did a bit of research and found the reason GitHub suggests this approach. RubyGems < 3.0.5 did not support GEM_HOST_API_KEY variable for gem push, and instead required the use of that credentials file. So this approach covers all cases. I don't expect we'll have such an old version of it floating about these days, so it's indeed safe to remove that aspect 👍