[storage] shrink default prune_window
[storage] shrink default prune_window

looks like it's common that people run fullnodes on volumes that are smaller than a few hundred gigabytes.

Closes: #6668

aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,libra/libra,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,libra/libra