[CI] Update codecov configuration file

[pedro-psb]

I've closed #990 but forget to create an issue about the codecov configuration issue.

Apparently, we should have a coverage.yml file for the Codecov app/github-action, but I'm not sure how this will go with local coverage reports, which seems to use .coveragerc. This require a little investigation.

The goal here is to have:

• a single config file (local reports and CI)
• an up-to-date configuration file (as recommended in codecov docs):
  • as a consequence, we can more easily customize the codecov config (if we discuss we need to)