docs: replace manual cov badge by codecov

[mdevolde]

docs: replace manual cov badge by codecov

Why the pull request was made

To have an external service that can reference the history of coverage of the repo, and provide the linked badge, without having to generate it manually.

Summary of changes

• Edit the CI to add the coverage report upload to codecov
• Display new badge in README
• Remove old generated badge

Screenshots (if appropriate):

Not applicable.

How has this been tested?

Not applicable.

Resources

https://github.com/codecov/codecov-action/

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update (changes to documentation only)
• Refactor / code style update (non-breaking change that improves code structure or readability)
• Tests / CI improvement (adding or updating tests or CI configuration only)
• Other (please describe):

Checklist

• Followed the project's contributing guidelines.
• Updated any relevant tests.
• Updated any relevant documentation.
• Added comments to your code where necessary.
• Formatted your code, run the linters, checked types and tests.

[codecov-commenter]

Welcome to Codecov 🎉

Once you merge this PR into your default branch, you're all set! Codecov will compare coverage reports and display results in all future pull requests.

Thanks for integrating Codecov - We've got you covered ☂️