Fix: private body in proposals

[Stef-Rousset]

🎩 Description

This PR adds the registering of private_body in create_proposal method from create_proposal_extends. As the rror spotted in production has not been reproduced in local env, this PR needs to be tested in production.

This PR also removes the override of FindAndUpdtaeDescendantsJob, because of the evolution of the code in 0.31 (notably 2 arguments instead of one in perfom method that causes error). The necessity of the override in 0.31 should be study in another card (cfhttps://github.com/orgs/OpenSourcePolitics/projects/26/views/1?pane=issue&itemId=186116483&issue=OpenSourcePolitics%7Cintern-tasks%7C443)

Testing

1. As an admin, in the BO, go to decidim awesome tab > Proposals custom fields > Private fields, and add some fields (screenshot one)
2. As a user in the FO, create a new proposal with content in private fields and publish it.
3. As an admin, go to the list of proposals, and for the proposal you created, click on "Answer proposal" button and check that the the private body is filled

📌 Related Issues

• Fixes https://github.com/orgs/OpenSourcePolitics/projects/26/views/1?pane=issue&itemId=175304829&issue=OpenSourcePolitics%7Cintern-tasks%7C411

Tasks

• Update specs

📷 Screenshots

ONE

TWO