Add Ender Dragon Kill Tweaks

[Invadermonky]

Add tweaks for hardcoded features of the Ender Dragon boss kill.

• Change first kill experience drop amount
• Change second+ kill experience drop amount
• Spawn Dragon Egg on second+ kill

These tweaks deprecate EqualDragons.

[what-the-diff]

PR Summary

• Introduction of Dragon Kill Management Feature
  A new feature that allows managing dragon kills has been added. This includes the provision to define the amount of experience points gained and the spawning rules for dragon eggs after each dragon is defeated.

• Updated Documentation
  The README.md file has been updated to include a comprehensive explanation about our new dragon kill feature to provide guidance for users on how it works.

• Added Configuration Options for Dragon Kill Feature
  A new category called DragonKillCategory has been incorporated into the "UTConfigTweaks" class. This helps users to manage various configuration settings related to the dragon kill feature.

• Modification of Experience Drops
  The UTEntityDragonDropsMixin functionality has been extended to adjust the level of experience drops from the first and second dragon kills.

• Dragon Egg Spawn Management
  A new mixin, UTDragonFightManagerMixin, has been created. This module allows for the regulation of dragon egg spawns after the first dragon kill based on the configurations set by the user.

• Addition of Language Keys for New Feature
  Reserved spots (language keys) in the en_us.lang file have been added for the new dragon kill feature. These keys provide accurate language descriptions that coincide with various aspects of the new feature.

• Registration of New Mixins
  Lastly, a new mixins configuration file (mixins.entities.dragonkill.json) has been created to register the new mixins associated with the dragon kill feature.