[IMP] l10n_be_hr_payroll_fleet, fleet: Adapt CO2 Tax up to 2019

Specification
=============

- Adapt the formula used in the code with the current legal value.
- Add the LPG fuel type in standard fleet module.
- Adapt the atn formula in the code with the current legal value.

Documentation:
https://finances.belgium.be/sites/default/files/downloads/121-faq-voitures-de-societe-2019-version17.pdf
https://www.socialsecurity.be/employer/instructions/dmfa/fr/latest/instructions/special_contributions/companycar.html

Description of the issue/feature this PR addresses:

Current behavior before PR:

Desired behavior after PR is merged:

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closes odoo/odoo#30484