[Codecov] Install codecov-cli instead of the Codecov uploader

[amenasria]

Why we're replacing the legacy uploader by the codecov-cli binary:

TL; DR: the 'uploader' has been deprecated since 2023 (see screen below). The right way to upload coverage files to Codecov now is to use the codecov-cli binary. I kept it before as it was the legacy way we were using Codecov, but we're now catching up with upstream because:

• We're missing interesting features:
  • Have the UI build URLs redirecting directly to our gitlab jobs.
  • Be able to get Codecov information right after you pushed to remote (this will be needed for later as it might be a mandatory check in the CI).
• Security
• Maintenance / ease of setup (doc is outdated sometimes)