Feature request

Feature description
Import option for converting PerWorldInventory-KT flatfile database to Multiverse-Inventories.

How the feature is useful
PerWorldInventory-KT went into archive mode and is no longer receiving development. Because of this, I would like to migrate off this plugin to Multiverse-Inventories but not lose my users' per world inventories. Would it be possible to add an option to migrate / convert?

https://github.com/EbonJaeger/perworldinventory-kt
https://www.spigotmc.org/resources/per-world-inventory.4482/

There is some work done in #433, but it's incomplete. It doesn't look like it's going to be completed anytime soon though, as we're all quite busy. We are of course always open to PRs though.