Resolve "The owner of a course can validate the good answer"

Description

If the owner of a course of an activity or resource considers an answer to a question to be correct, he can validate that answer so that it cannot be deleted.

Migration and compatibility

• The merge request DOES NOT update the models. If it does, database migrations are needed after merging, add the label Database migrations
• The merge request DOES NOT break the compatibility.

TODO

Before being accepted, any merge request must fulfill the following requirements:

• Check PEP8 writing style as described in CONTRIBUTING.md.
• Ensure existing tests are still working properly.
• Features have been tested.
• Every translatable strings are written in proper english.
• Every translatable strings are tagged for translation using gettext, blocktrans and/or trans.
• Ensure that there is no side effect in files: changes are only related to one, and only one feature.
• Ensure that no file has been removed by accident.
• API is documented, as well as the behavior, if needed, in docs.
• Ensure the commit history is “clean enough” (this means no extra merge commits, etc).
• Ensure pipeline succeeds.

git checkout <feature_branch>  # Switch to the feature branch
git fetch --all --prune  # Download new commits
git reset --hard <remote>/<feature_branch>  # Override your local worktree with the one from remote branch

Impacted Areas in Application

(list general components of the application that this merge request will affect)

/label Status::In development /label Needs review