Fix maturin deployment to PyPI

[felixhekhorn]

Left over from #375:

Fix secrets for maturin

@felixhekhorn we will need an API token to publish this. One already exists, but I believe has its scope limited to the eko package, so it's not useful to publish the eko-rs wheels.

Unfortunately, I can not login any longer on PyPI N3PDF account, since they are now enforcing 2FA. I guess we'll need to ask a token to @scarrazza or @scarlehoff

Originally posted by @alecandido in #375 (comment)

Generalize workflows

since I may serve the script from https://github.com/NNPDF/workflows, instead of this repo.

[scarlehoff]

Just let me know when you want me to produce the token.

Or even let me know when you want to log in and I can give you the 6 digits code to login

[alecandido]

Just let me know when you want me to produce the token.

If you can, immediately. Or as soon as you can (you could even store by yourself among secrets, as PYPI_TOKEN_MATURIN, or something similar).