ci: Add initial code coverage report

[chtruong814]

What does this PR do ?

Add initial code coverage report based on unit tests only for now.
It does not upload anything yet. We can enable that when the repo goes public. It also excludes the /tmp ray files from being considered for code coverage.

Issues

#219

Usage

• You can potentially add a usage example below

# Add a code snippet demonstrating how to use this 

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Additional Information

• ...

[terrykong]

lgtm. just had comment about moving configuration, also you'll need to rebase to take account of the repo name change

[chtruong814]

@terrykong updated. Please take another look.