[MIG] agreement_legal: Migration to 15.0

[etobella]

Superseeds https://github.com/OCA/contract/pull/825 as it has changed the repo

TODO:

• [ ] Add a migration script to migrate data from Jinja2 -- Should be similar to what is done on OpenUpgrade or OpenUpgradeLib

@marylla

[dreispt]

/ocabot merge nobump

[OCA-git-bot]

Hey, thanks for contributing! Proceeding to merge this for you. Prepared branch 15.0-ocabot-merge-pr-3-by-dreispt-bump-nobump, awaiting test results.

[OCA-git-bot]

Congratulations, your PR was merged at 372a819b7436ebc01d44d0c28d262aee3b413739. Thanks a lot for contributing to OCA. ❤️