Add Coveralls test in CI

[marilyn79218]

As title

Steps:

1. Use jest --coverage to generate coverage report in CI step.
2. Add this repo to Coveralls. See screenshot-1.
3. Will see instruction when you click on the details button in screenshot-1, and it redirect to screenshot-2 where it says you should add .coveralls.yml for it.
4. Generate Github perosnal access token at Github page. Use your repo token shown in coveralls page (e.g., https://coveralls.io/builds/<build_id>). See the token shown in screenshot-2.
5. Add the token just generated in the .coveralls.yml.
6. Push your changes to Github that triggers test and coverage/coveralls CI checks.
7. Coverage data is passed to coveralls page as shown in screenshot-3.

Sidenotes:

• When you click on Documentation button in screenshot-2 (at page bottom), you will be redirected to screenshot-4 (Coveralls getting started page).

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[marilyn79218]

Note: the GITHUB_TOKEN is built into Github Actions and does not need to be manually specified in your (repo) secrets store. See screenshot.

See Coveralls GitHub Action or Github doc.

[marilyn79218]

Successfully run coveralls in CI checks