Add check for copyright headers

[rubennorte]

Summary

Added a script to verify that source files contain the Facebook copyright header. Facebook has an internal tool to verify it and will help aligning them.

Test plan

echo '// Non-empty' > packages/jest/foo.js
git add packages/jest/foo.js
yarn run check-copyright-headers

The output should be something like:

Facebook copyright header check failed for the following files:

  packages/jest/foo.js

Please include the header or blacklist the files in `scripts/checkCopyrightHeaders.js`
error Command failed with exit code 1.

And the exit code must be 1 if it failed and 0 otherwise.

The lint-and-typecheck job should check this. Example: https://circleci.com/gh/facebook/jest/39078

[github-actions]

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