Add the ability to configure multiple join items.
Update existing functionality to allow to add / remove items from the list.
Each entry includes:

• Material
• Amount
• Label (Optional)
• Unbreakable (default to false)

Command "/pa addjoinitem (course) (material) (amount) [label] [unbreakable]".

Example "/pa addjoinitem tutorial Elytra 1 &6Wings true"