[Tests] Add coverage badge

[inimaz]

It would be interesting to run the coverage in the CI and have a coverage badge that gets updated.

[salob]

@inimaz I see a lot of workflows here:

https://github.com/mlco2/codecarbon/tree/master/.github/workflows

which one is considered the continuous integration build

Thanks

[inimaz]

Hi @salob, we have these:

• To run the tests of codecarbon pypi package: https://github.com/mlco2/codecarbon/blob/master/.github/workflows/test-package.yml
• To run the tests of the API carbonserver: https://github.com/mlco2/codecarbon/blob/master/.github/workflows/build-server.yml#L29

We could have a coverage badge for each of them.