Publish to npm from GitHub actions

[nicolo-ribaudo]

Q	A
License	MIT

Closes #10663

During GitHub Universe 2020, they presented environments with manual approval for GitHub actions: regardless of who has write access to this repository, we can now granularly configure who has access to a given secret.

I gave access to @JLHwung, @existentialism, @hzoo and me.
Currently the stored NPM_TOKEN is mine, but it it works we should use @babel-bot's.

Now the publishing process is just this 🎉

# Create a new release commit
make new-version

# Push to GitHub
git push --follow-tags

I'm testing this action in the second commit (I'll revert it before merging), publishing an empty package.
This is what the UI looks like: https://drive.google.com/file/d/1q-kCP7rp-7UKZZfChrI3v-s2iVHi0KDE/view

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/35823/

[nicolo-ribaudo]

This works 🎉 🎉 🎉

Workflow run: https://github.com/babel/babel/actions/runs/430661855
Published package: https://www.npmjs.com/package/@nicolo-ribaudo/babel-publish-test (I released 0.0.1 locally, and 1.0.0 from this action)
GitHub release (if you have write access to the repo): https://github.com/babel/babel/releases/tag/untagged-6839561d8e388548b3b7 - This is completely wrong, but it's just because I didn't push a tag to this PR so the release tool generated the wrong changelog.

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit a7bd3ba:

Sandbox	Source
babel-repl-custom-plugin	Configuration
babel-plugin-multi-config	Configuration

[nicolo-ribaudo]

Note: This line is the only untested step in this PR (I commented it out, run the action, and everything worked). However, we test in in the e2e tests on CircleCI where we publish to verdaccio.

[JLHwung]

Q: Is fetch depth 0-based or 1-based?

[nicolo-ribaudo]

It's 1-based, 0 means "fetch all". We need it in order to find the previous tag.