feat(detections): add bboxes column to detection and a route to fetch unacknowledged ones

[RonanMorgan]

Add the acknowledged boolean in the table Detection and a new endpoint. It will allow the plateform to know if a Detection has been acknowledged by a User.

[frgfm]

Thanks! High level question:
@MateoLostanlen @pyronear/front-end what is the minimal necessary information we need about unacknowledged détections?

I think it's a fallback until we have proper notification system. But let's make sure we get the exact thing right:

• do we plan on letting users specify a time range?
• if not, what's the time range? Last 24hours? Longer?
• if there are too many (and there will), how many should we keep and in which order should they be? (The N latest, the N oldest)

[frgfm]

Thanks! I added a few comments!

[frgfm]

Here is a recap, after modifications, of what the PR introduces:

• add a "bboxes" string column in the detections table, regex verified to avoid troubles
• add a route to fetch unlabeled detections
• update the client accordingly, and add a fetch_unlabeled_detections method
• update client, backend & e2e tests accordingly
• for migrations, only a minor fix, we'll create a clean one once we have enough to release & deploy (better to have 1 migration per production deploy)

[frgfm]

cf. #304