Use PyPi token for authentication on CI deploy job

[sandcha]

Context: 2FA Requirement for PyPI begins 2024-01-01

• Technical improvement.
• Details:
  • Use PyPi token for authentication on CI deploy job
  • Allows for Python package upload since the 2FA enforcement on PyPi

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This PR comes with:

• on PyPi: a PyPi token linked to this repository added to a PyPi account having access to the OpenFisca Extension-Template project (the token is on the openfisca-bot account; we can find it on the settings page)
• on GitHub: a PYPI_TOKEN_OPENFISCA_BOT in this repository secrets

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These changes :

• Change non-functional parts of this repository (for instance editing the README)

[MattiSG]

Let's already check that everything works well in openfisca/country-template#144 before backporting here 🙂

[sandcha]

Regarding 49f5c97 @MattiSG, I think that it's better to revert the commit.
I don't understand what happened to the PYPI_TOKEN_OPENFISCA_BOT in this GitHub repository secrets settings (if we revert the commit, we need to set it back in the settings) but I think that we need to keep the user account name in the token name (like OPENFISCA_BOT here) to avoid the issue that we had at the beginng of this year (finding the PyPi user that added a PyPi token and the kind of configuration that was made on the PyPi user account interface).

[sandcha]

The PR is ready again for a review @MattiSG @benoit-cty.
Regarding configuration, there is a new token:

• on the PyPi openfisca-bot account (I removed the previous one from PyPi)
• and in this repository settings (PYPI_TOKEN_OPENFISCA_BOT ; I also removed a PYPI_TOKEN from this repository secrets).

And I didn't revert the 49f5c97 commit in order to keep its syntax.

[sandcha]

Thank you @benoit-cty! Reordering commits and merging...