store/rootmulti: Add a cli cmd to prune old states according to current settings

[yihuang]

Summary

When updating pruning settings, the old states are not pruned automatically.
While there were efforts(#10942, #11064) to do that automatically on initialization, it would be helpful to support offline pruning through CLI command as well, which should be easier to implement.

Problem Definition

Proposal

[tac0turtle]

This is amazing, thank you