Periodically fetch and save propositions to enable full text search afterwards

[kimuraz]

Describe the solution you'd like
One big differential we could provide by using this backend is to offer full text search, since it uses postgresql, the feature is half way there.

Describe alternatives you've considered

Uses either postgresql or something like elasticsearch (although the costs for deployment of a node + backend would not be nice) and a new endpoint on the backend side to enable the feature.

Open to discussions of course.

CC @alexandreab