Set blocks preservation cycles to 1

Context

based on !11300 (merged)

Moving blocks preservation cycles from preserved_cycles to 1, so that the shell can garbage collect more blocks.

1 ensures that it keeps at least one full cycle, which is better in term of UX. If relevant, we could later go down to 0, so that it can just keep the blocks of the current cycle.

Manually testing the MR

Checklist

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