Offer data or subset of data before it gets pruned #3775
Description
When storage-capacity of a Portal node is about to be hit, currently data just gets pruned.
Although this is currently not mandated by the specification, it might be useful to offer a set or subset (e.g. n content items closest to the content id) of the to be pruned data before actually deleting that data.
The reasoning here is that the only mechanism to redistribute certain data over newer nodes is the POKE mechanism. But this only activates on external trigger when data gets requested but is not found on nodes which match the radius. So if it is data that never gets requested, it will also not be redistributed.
This is somewhat related/complementary to ethereum/portal-network-specs#350, but a bit easier to add.