Terms and conditions refactoring

[lunika]

Feature Request

Is your feature request related to a problem or unsupported use case? Please describe.

Terms and conditions (CGV in french) must be specific for every organization. This means that we can't have a global one for the whole platform.

Describe the solution you'd like

• Terms and conditions will be included in the contract definition provided by the organization.
• There is no more need to accept them in the sale tunnel, they will be signed in the contract (remove this part).
• There is no more need to store in the order model if the user accept them (remove it from the model).
• There is no more need to store them in the site model in joanie and in richie.
• There is no more need to inject them dynamically in the contract, they will be already present.

[jonathanreveille]

This issue has been solved and merged into the dev branch https://github.com/openfun/joanie/pull/831