1. Added showcase.use.view permission.

• This permission allows the player to view showcases (including their own), but not edit their own showcase.
• Thanks Wratek for the suggestion!

2. Showcases now get created automatically for a player when they join the server if they don't have one.

• Before it would only create a showcase for the player when they run /showcase for the first time.

3. Added official support for Minecraft v1.20.6.