Add a config option for what rank can do upgrades

[JHarris12345]

So for a command upgrade we are giving permissions to upgrade member count (not sure why its not a default upgrade). But that means if a member does it (not the owner), they get the permission and not the owner
so if the member leaves.... the owner is screwed
would jsut make it 100x easier if you can make it in config set what rank can do upgrades

[Guillaume-Lebegue]

For adding it natively to upgrade, I will need BentoBox to give a way to update this number and I didn't found it.

Else, the command upgrade was updated, you can now use island owner as a placeholder, so you can give permission to the owner. But be careful with that, as when the owner resets the island, It's permission won't be.