Setup Codecov

[lesterong]

What is the purpose of this pull request?

• Documentation update
• Bug fix
• Feature addition or enhancement
• Code maintenance
• DevOps
• Improve developer experience
• Others, please explain:

Overview of changes:

Generates coverage report from each package and uploads to Codecov using GitHub actions. Codecov report can be found here. Resolves #1755.

Anything you'd like to highlight/discuss:

• In packages/cli, we don't run all the tests using Jest, looking into how to generate the coverage report for that properly

Testing instructions:

N.A.

Proposed commit message: (wrap lines at 72 characters)

Setup Codecov using GitHub actions

---

Checklist: ☑️

• Updated the documentation for feature additions and enhancements
• Added tests for bug fixes or features
• Linked all related issues
• No unrelated changes

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@d6ad99d). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2348   +/-   ##
=========================================
  Coverage          ?   44.82%           
=========================================
  Files             ?      122           
  Lines             ?     5133           
  Branches          ?     1082           
=========================================
  Hits              ?     2301           
  Misses            ?     2513           
  Partials          ?      319           

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[tlylt]

In packages/cli, we don't run all the tests using Jest, looking into how to generate the coverage report for that properly

Related to #771. @lesterong I think it's ok if we can't get those coverage stats for now, which should be easy to add when 771 is resolved.

[tlylt]

can we add the badge as well