PITR: Flow history retention interval settings from the master

[bmatican]

Since history retention dictates how many versions we keep in MVCC, we need to ensure that snapshots are taken at a regular interval, which should be smaller than the history retention window.

However, we definitely cannot ensure that users would respect that. Even if we end up doing this ourselves, internally, we might still end up with delays or the snapshotting might get jammed for various reasons (ie: bugs?).

An easy solution for this then would be to just make sure we have the master can force an increase of the history retention on the TS, if PITR data integrity could be affected.

[bmatican]

Done as part of
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