[Content nodes] Rationalize the use of timestamp-relative columns in data_sources_nodes

[aubin-tchoi]

• Follows up on #9849 and this thread.
• We have a column timestamp in data_sources_documents and data_sources_nodes that is currently filled by connectors with lastUpdatedAt and filled by other users of api/v1 by whatever.
• We need the lastUpdatedAt information to fill the content nodes.
• We currently use the timestamp column to fill this lastUpdatedAt in front.
• Depending on what we observe about what the users do, we need to update the name of the column.

[aubin-tchoi]

Pending because we need to observe the logs regarding what the users of /api/v1 do.

[philipperolet]

Thanks for creating the card 🙏 Plan would be to:

• look at logs of this after a week;
• hope we don't have any user-set timestamp, if not rename bluntly
• if we do, warn related users, deprecate the field (so leave it working but mark as deprecated in favor of a lastUpsertedAt field)

[philipperolet]

Moving to eng runner and assigning us @aubin-tchoi , not necessary for the ship + needs some waiting so we can't act now anyways