Get rid of unwrap/panic in database providers in aggregator

[jpraynaud]

Issue

We want to avoid unwrap and panics in database providers code. These unwrap panics should be replaced by a specific error type that will be gracefully handled as critical error by the state machine.

To do

• [ ] Try to implement critical error detection at the top with downcasting of error with anyhow (and define common errors for modules, e.g HydrationError for all database providers?)
• [ ] Transform all the unwrap in errors in non test code (and let the top caller decide: e.g. panic if in state machine runtime and error 50x in the HTTP server)

Linked issue

Relates to #798