Refactor jobs pipeline to hydrate data from snapshots

[mhd-hi]

Current

Data hydration works as follows:

1. Fetch data from source inputs (PDFs, cheminements.txt, APIs)
2. Parse the data
3. Save it to database

Goal

Change this pipeline so hydration happens from snapshots instead of directly from source inputs:

1. Save data as a snapshot
2. hydrate the backend from that snapshot only

This should make the data aggregation pipeline easier to maintain.

(Attributes planificationPdfJson and horaireCoursPdfJson was a good start but never fully implemented, remove it and create table.s containing snapshots)