[IMP] Taxes: improve tax configuration doc

task-5094417 This commit rewrites the Taxes page. Previously, it came across as a huge list of tax configuration options. We now structure it as follows: 1. an overview of the tax flow in Odoo; 2. a set-up guide for taxes for new users; 3. an explanation of the most common configuration options. The options related to the tax computation are split into a separate Tax Computation page, in which we also improve the following sections: - Tax computations: At the moment, the section for the `Percentage of Price tax included` tax computation doesn't distinguish itself enough from the 'Included in Price' option which people usually want. We also improve the examples. - Included in Price - Affects base of subsequent taxes - Base affected by preceding taxes: this option was not documented, so we add a section for it. Ultimately, we plan to rewrite the Tax Computation page to provide a better explanation of how the tax computation actually works, and be more helpful at guiding the user to configure their taxes. X-original-commit: 0f67d04

Author: antoine162