Persistent Bossbar Command

Add a new parameter to bossbar commands that will make the bossbar command static.
Along with it, add a command to remove bossbars from the player.
- `/bossbar remove player`
- `/vbossbar remove player`

Look at existing bossbar command implementations in the codebase, likely in a command handler or bossbar manager class. Understand how bossbars are currently created and managed for players. The new parameter should make a bossbar persistent (static), and a remove command should clean it up. Test by running the plugin on a Paper or Velocity server and verifying the new commands work.

Written by the indexing model from the issue text.