Add official 1.20.6 support

[NonSwag]

Description

This PR adds official support for 1.20.6

• cloud command framework was updated to utilize the latest addition of paper brigadier
• use gooolers shadowJar fork for java 21 support
• updated hangar publish and removed dead code from publication task
• updated workflows to use java 21
• removed dead versions from "supported" list

Checklist

• I included all information required in the sections above
• I tested my changes and approved their functionality
• I ensured my changes do not break other parts of the code