[FEAT] Extend the KubeJS plugin to make persistent data savable inside of the library

[BanditHelps]

Right now, the data saved using player.persistentData inside of an addon does not make the data accessible to the library mod. Therefore, things like custom placeholders do not have access to them. This feature will make it so that the data is synced to the library, and can be used accordingly.

1. Create a new KubeJS function that accepts a <key, value> pair, and stores it into the server players persistent data.
2. Make sure to have functions to retrieve it as well as store it.