Update codecov upload to use node-based uploader

[Vogel612]

codecov/uploader is replacing codecov/codecov-exe (which we have been installing via chocolatey) and because support is dropped on February 1st we need to actually migrate

[Vogel612]

The migration is finished, unfortunately I have not been able to get appveyor to verify the GPG signature to make sure we're not downloading some sort of malware 😟

As such this issue remains open to make sure we probably maybe at some point fix that.