[back] feat: add entity contexts to unconnected entities API

[GresilleSiffle]

related issues #1852

---

Description

This PR adds the support of entity contexts in the unconnected entities API.

Moreover the logic used by the comparisons API and the unconnected entities API has been factorized in PollScopedViewMixin. Now all poll related views can access the entity contexts directly from self.entity_contexts.

to-do

• update the tests

Checklist

• I added the related issue(s) id in the related issues section (if any)
  • if not, delete the related issues section
• I described my changes and my decisions in the PR description
• I read the development guidelines of the CONTRIBUTING.md
• The tests pass and have been updated if relevant
• The code quality check pass

[amatissart]

What are the cases where poll or ent_contexts would be None ?

[GresilleSiffle]

The ExportComparisonsView class uses the ComparisonSerializer to write the comparisons of the logged user in a .csv file. In this case the serializer context doesn't contain any entity context.

If we consider that a comparison should not be represented without its related entity contexts, then we may want to remove this condition and ent_contexts is not None. In this case we should also consider adding the entity contexts in the public dataset.

Because they are here to "bias" the comparisons I think it could be a good idea to include those entity contexts in the public dataset.

[GresilleSiffle]

I created an issue to address this question #1902