add step to publish coverage to codecov.io

[AlexVCaron]

Quick description

Publish coverage reports to codecov.io after testing

...

Type of change

Check the relevant options.

• New feature (non-breaking change which adds functionality)

Provide data, screenshots, command line to test (if relevant)

Report on Codecov.io

Checklist

• My code follows the style guidelines of this project (run autopep8)
• I added relevant citations to scripts, modules and functions docstrings and descriptions
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I moved all functions from the script file (except the argparser and main) to scilpy modules
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[arnaudbore]

Build passed ! Good Job 🍻 !

[codecov]

Welcome to Codecov 🎉

Once merged to your default branch, Codecov will compare your coverage reports and display the results in this comment.

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

[arnaudbore]

Build passed ! Good Job 🍻 !

[arnaudbore]

M.A.C.H.I.N.E